One-way rentals in Florida are usually much cheaper than elsewhere in the USA (sometimes the same price as "regular" rentals), but I encountered high prices on recent rentals from TPA to MCO and between MIA and FLL. For some reason, in Florida, the AMEX "friends and family" rate seems to produce the best rate of the National codes -- about $25 for a midsize on the Emerald Aisle (which is likely to be better than a midsize).
If you rent for 2 days including a Saturday night, you can attach Coupon ND8435DJD for another $10 off -- making it a pretty good deal for a weekend rental. There are probably other coupons that are better, especially for longer rentals.