Ditch the car. Fly to NYC. Snow in Dec. is mostly in upstate NY, Syracuse etc.
I just flew from Miami to NYC in 3 1/2hrs; you'll drive 2 days. Want 100% snow? Visit Canada or Europe in Winter.

I have never heard of any American auto rental company restricting rentals to the state in which you pick up the car. I think that just never happens. However, if you plan to drop off the car in any place different from where you pick it up, you may have to pay an additional fee, and you'll have to make sure that you have arranged the one-way rental in advance, because some cars may not be available for one-way rental.

i always use Enterprise and IM SURE they have that restriction----sorry i made it a general statement, i was only trying to alert the poster to question it.
On the 2nd point about drop off,you have to have as part of your agreement that youll be using the car one-way and designate the drop off location, and the fees--if one doesnt, its called "theft by taking".and its a felony if the rental car company cares to press charges

The rental car driving range is more often regional - like limited to 8 southeast states if you pick it up in Florida. I often rent a car in North Carolina, drive it within that state only, and one day actually read the stuff I signed and I was limited to general area from Florida to Virginia for where I could take the car. So while not being able to take it out of state is unusual, regions are not.

Some cost factors you need to consider - when you see rate for type car you are renting, there are often additional taxes/fees. Renters from outside US often have to pay for all the "optional" insurance. And then, as mentiaoned above, the one-way rental/drop off fee - which driving a car north from Florida in December is likely to be substantial.

Just make sure you know all the charges before you pick up car - so there are no surprises.

And for the trip - I95exitguide.com lists all sorts of hotels, attractions, restaurants right along most of your route.

Thank you all very much for your all of your advices! Specially on the driving stuff!!About the confort of the car...I'm pretty sure an accent will do it just fine, I drive a similar one here in Costa Rica, and we fit fine in it. We're not taking lots of luggage, so I don't think size must be an issue.
About flying, it was our first option, but then we decide we plenty of time for several stops, so we plan to see different places on our way north. As a matter of fact, we want to make a stop in Savannah, North Carolina, and Washington prior arriving to NYC. I'm an architect, so I'm really looking forward to it.
Now my concern is about parking, I haven't actually thought about that before, but gonna figure out something -Hope so, at least!!!!
And by the way, I'll check if Hertz has the state restriction, though I LA last year and went to Vegas, and the Grand Canyon with a Hertz car. They never told there was any problem...but I'll check for sure.

Yin, if you're still out there... I guess if you're planning to visit Orlando, Savannah, Washington DC, and someplace in North Carolina, then you've certainly planned a trip that will be more economical to do by driving, rather than multiple plane tickets.

It's hard for me to imagine four adults being comfortable in an Accent for 2+ weeks, but if you can do it, that'll help a lot with expenses! I'm glad that you're not feeling dissuaded by the winter driving, because it really won't be a big deal.

As you're planning to visit Savannah anyway, I wonder if it might be interesting to proceed on smaller roads up through Beaufort, SC and up into Charleston, SC, before returning to I-95. I've never visited this part of the U.S., although I've always wanted to. Maybe someone can weigh in regarding what this area is like in December.

Definitely return the car as soon as you get to New York City. You won't want to use it there, and you'll just end up paying more money for a longer rental, and for a parking space that may be expensive. DC is the only other place where parking is likely to be a significant issue. I'm sure some Washingtonians here can help with that if given a few more specifics about the trip.

It would not, IMO, be the least BIT "unusual" to have possibly snow, ice, and the stupid jerks who think they can drive 100 MPH in it because they have "four wheel drive" in December on 95.

Yes, it was somerwhat "unusual" that we had two major snowstorms in less than a week here in the Metro Washington area last February BUT we HAD them.

I think perhaps this may be a time for the OP to do some in depth analysis of the real costs of the proposed trip INCLUDING time.