As some others have posted, there is a good chance for a decent price on a one-way rental depending on the direction and time. I just looked at a
3-day rental from Orlando Airport to Groton, CT with
budget for June 9 and the price is
$75 total for a full-size car.
That's not including fuel and if you need to stay overnight though. At 1200 miles, the fuel cost alone is $160-ish at 30 MPG, and goes up depending on how fuel inefficient your vehicle is, and figure another $60 for an overnight stay in a Motel 6, plus you have tolls (about $40 between NY and NJ) and you're getting close to $300, and that's for a super cheap rental and doesn't include the food costs of spending another day away from home, which isn't insubstantial either.
As a fellow CTer, if you're really looking to save money, check into Amtrak. Not just the Auto Train, but they also offer service from New Haven or any number of other CT stops to Orlando with a train change either in NYC Penn Station (NYP) or DC's Union Station (WAS). Depending on the time of year, you can get a family of 4 in a sleeper compartment for $400, and that includes meals. Since it travels overnight, you don't lose the same amount of time that you would driving, and you arrive far more rested.
Alternatively, you can hit dozens of area airports easily from CT. BDL, HPN, LGA, JFK, BOS, PVD, EWR, and HVN all offer direct or two segment (only one layover) flights going down. CT is unique in having access to so darn many big airports without adding much drive time. Doing an open jaw itinerary (departing from and returning to different airports) can frequently save a considerable amount of money. You do have the issue of getting to and from the airports, but cashing in a favor from a friend, or taking rail+bus or rail+taxi is a bit time consuming but cheap and always an option.