I think you may have to adjust your budget upwards or go at a less expensive time of the year (which, I know, is difficult with teenagers school schedules). Spring break would likely have been les expensive than May but it is probably too late to take advantage of any fare sales...

I use www.itasoftware to search 30 day periods for airfare. You might find that helpful too. Click "Lookig for airfare" then "guest log in" then at the top right is a 30 day search.

I have flown direct from CVG to CDG twice in the past but have noticed far fewer direct flights from Cincy (and more expensive to boot) than previous years.

There are several websites showing tickets just under $800 including taxes and fees for the end of May. Check with some of the websites that check prices at several websites at once, like www.kayak.com and mobissimo.com

If you paid, let's say, $790 each for air (and you might find something on sale for a bit less than that in the next month or two), that would leave $210 times 3 people or about $630 for accomodations. I did a quick search on www.hrs.com, and it came up with several 2-star hotels that would be within that price range for 3 in one room for 5 nights including taxes and breakfast--barely.

I you'd be willing to share a bath down the hall or consider B&Bs or rooms in private homes, then you might do even better and perhaps make it for 6 nights.

Of course, there could be some air/hotel packages that fit, as well, but I'll let you search those out.

Just don't expect a sumptuous buffet breakfast, a location next to the Louvre, or on-site gym and pool.