austin actually has tons of cheap rooms. the best deal being the hourly rooms over at musiclab (2 locations) prices range from $7 an hour to $14 an hour for rooms with full p.a's and monitors http://www.musiclab.net/rehearsals/
it is really common for bands starting out to meet up here for rehearsals/jam sessions. it really isn't that much everybody chips in a couple bucks and rents the room for a few hours. they also rent rooms out for the month, but I don't know their rates.
also has rooms available for monthly rental starting at 400-600 a month.
in houston lockout monthly rooms are cheaper $350 a month.
I know dallas and san antonio haver similar options for rehearsal studios.