A quick check at Expedia.com for some random dates in May showed around $650 to rent a mid-size car in New York and return it to Orlando 1 week later.
I'm sure if you look around for deals, you could get it lower than that. Make sure you look at the total price for anything you look at because it looks like different companies do it differently.
For instance, for the search I did, Budget shows a rate of $71 per day with a total price of $650. Dollar shows a much lower daily rate of $43 per day, but has a total price of $872. So it looks like some companies raise the daily rate for one-way rentals, while other companies keep the same rate, but add on drop-off fees or one-way fees.