One other thought @:-)

Renting off airport can save a lot of money (pretty much all US cities have stiff taxes for hotels and airport rentals).

I've done this at SFO, and if it's enough days, you may well save enough money for taxi from HOU to rental location, and then drop off somewhere in Humble / north Houston area and still come out ahead.

One other thing I've been able to do is to use same location for pickup and return when booking, and then call to see if I can drop off at "co-terminal."