Keep in mind that with only 16 days you have 3.5 days in each city which is not a lot of time in Vienna, Budapest, and Prague (haven't been to Zagreb so can't comment on that).

If you hire a car and driver and stop overnight you need to pay for the driver's lodging and food plus the cost of the car service.

A better option would to take a day drip from one of these cities to someplace you're interested in. For example: from Prague, a day trip to Kutna Hora or Cesky Krumlov. From Vienna, a day trip to Melk. This way you're not adding a one night stay over which can take more time than expected and you're only staying in 4 hotels, rather than 5.

You can easily take a train between all of these cities (approx a 5 hour journey for each leg), relax and enjoy the scenery. Grab some food at the train stations or other places before boarding the trains and have picnic lunches (don't forget the wine and corkscrew!). It can be lots of fun to do this and much cheaper.

What would be afffordable to you? You are obviously looking at thousands of dollars plus fuel.

Two questions: (1) What's the fascination with Zagreb? Based on reading others' discussions (haven't been), it's better used as a gateway to the rest of Croatia (read: primarily Dalmatian Coast or short flight to Dubrovnik) than as a destination.

(2) How many of you are there?

You do know that there are trains in Central Europe, right? They're not the fastest, but they do work, are far less expensive for 2-3 of you than a hired driver you're paying to cart you 4-6 hours from his home, and take about the same amount of time.

And for your Vienna-Budapest leg (whichever direction), you can use the Danube River hydrofoil. It's a 5.5 hour run on the boat (the train takes less than 5 hours). http://vienna-hydrofoil.hotels-in-budapest-hungary.com/timetable.html

You need to set the schedule properly. If you decide to go to Zagreb, you need to go Prague-Vienna-Budapest-Zagreb or reverse to minimize the transit times. If you stick with the main three (each of which likely deserves 5 nights - I know Budapest and Prague certainly do), then Prague-Vienna-Budapest or reverse. From Budapest you can day trip to the Danube Bend towns or Western Romania; from Prague you can day trip to Karlstejn Castle, Cesky Krumlov (do this by private car), Terezin, and more; from Vienna, Bratislava is only an hour away.

Open jaw fares should not be much more expensive, if at all, than RT to Prague/Vienna/Budapest (forget Zagreb as a RT destination). If they're within $300 of each other (which they should be), take the open jaw and save yourself the hassle.

If you want the flexibility to just pop in for a night in _____, then rent a car and pay the drop charges. Seems uneconomical. That said, you can more easily take day trips from your base cities (including hiring a driver) than just stopping in some little hotel in the countryside for a night in a town whose name has lots of consonants.

Thanks all for your replies.
To answer some of your questions:
We have Zagreb on our list because my husbands grandfather is from there and he'd like to see it.
There are 4 of us traveling.
Day trips from the base cities sounds like a good idea. We love car trips and the ability to stop when and where we want but this may not be the right situation to do that. Especially with the cost involved.
Thanks again....I appreciate your help.

Some friends of ours did rent a car and did the cross-border drop off. They did not consider it that expensive, as the cost was divided 4 ways. This might be a way of looking at a car rental that covers more than one country.

Michael....do you know what rental car company they used and the countries they visited....?

I do not know the rental agency, but they started in Slovenia or Hungary and ended in Germany.

Glad you explained the reason for going to Zagreb, as I found there wasn't much for a tourist to do there for more than one day.

Might you consider a train-car combo? You can train between the cities you mentioned and then rent a car say in Prague and drive around the Czech Republic, then return the car in Prague and train to the next city.

For example, the German rail website, bahn.com , has a section on train-drive options.

On the other hand, you could rent a car and do all the cities by car. Of the cities that you mentioned, the only one I haven't driven to is Zagreb. Otherwise, the roads are usually pretty easy to negotiate in that region. The only problem is driving in town. I hated driving around Budapest.

There's all kinds of permutations for your travel plans. You didn't say what your budget would be, but hiring a driver and car to do all those cities will not be cheap.

> We love car trips and the ability to stop when and where we want but this may not be the right situation to do that

I think you might do well to consider the possibility that this really isn't the best itinerary for car trips. You plan to visit several truly wonderful cities that could each easily warrant more time than you give them. I've been to all 4, and spent (as I recall) about 3, 3, 4, and 3 days, respectively, in Zagreb, Prague, Vienna, and Budapest, not counting travel time or time outside the cities themselves. But people travel for such different reasons that I think it is hard to say how much time anyone else will want to spend somewhere. (As an example: many people apparently give Zagreb only a few hours or a day at most; I wish I'd had more than the 3 days I gave it. I think it is quite underrated. Just my opinion.)

The train rides between these cities would give all of you a chance to relax and enjoy the scenery.

But again, it depends on what all of you want to see and experience!

You are planning to visit some wonderful places - enjoy!

Reflect on your 'fear' of the cost of a car rental:

Your airfare will be $1,000+/per RT = $2K
Lodging, $100/nite = $1.6K
Food, $100/day = $1.6K
Underestimating the above = $5K

Total about $9,000

Cost of a rental car (some multi-company rentals ARE available, but you have to ask, not await an answer to an un-asked question) might be $800

if cost of trains were only $500, then you'd be concerned about $300 difference on a $9,000 base, in other words, a 3% difference.

My feeling (having driven in all those countries) is, see what you want, how you want, to maximize your enjoyment, and don't nickel/dime trivial differences in cost. Personally, I like the freedom to stop where I please; small towns often offer amazing surprises.

The trip is doable by car, and the cost of parking/garaging, though not low, is acceptable - something like 15 to 20 euro a night.
If you are flying into and out of one city, say Vienna, it's a simple of job of picking up your car at the end of your stay in Vienna and driving to your next destination. You will have to tell your rental company you are driving into Croatia (outside EU and Schengen), as some may not allow it. You are probably ok with other countries (including Slovakia which lies between Hungary and Czech Republic) but you should tell them. A car rental broker like Auto Europe has vast experience in cross-border rental and should be able to arrange a rental with a suitable company.
Watch out for road tolls on expressways - each country has a different tariff and charging system.