ill bet there are more areas to ride in the austin area than here in houston. but id bet the majority are pay to play. i wouldnt suspect more than 15 a day though. best ive seen is barnwell mountian right outside of gilmer texas cant remember where austin is to that), its like a 5 hour drive for me. i used to live right north of bakersfield, 2.5 hours from the coast. didnt have anything to wheel in those days however. pretty much an hour in any direction to wheel/ATV/dirtbike were im at.
I live in Austin and I can tell you with confidence that you're going to be very disapointed with the limited places you can go play. There are some places (I think someone mentioned Gilmer) but they are several hours away and will require a whole dedicated weekend at least. I have never been to any of them so I don't know about the cost or if it is worth the money. There is virtually no public land in Texas - it is all private deer lease ranch dirt farmer stuff. Most other states I've visited you may experience this scenario: Driving down the highway and notice a 2-track up on some hill. You think to yourself, "Self, I wonder how to get there...and where will it take me?" Eventually you see a dirt road intersect the highway and off you go. If you do that in Texas you will most likely be tresspassing and may get some 00 buck in your a$$ for your trouble. I hate to say it, but Texas is not very OHV friendly.
I lived in San Diego and logged many miles in the BLM lands. I now live north of Austin. My favorite place is Padre Island National Seashore south of Corpus Christi. There is 65 miles of undeveloped beach that is the closest thing to getting away from it all that you will find in Texas. The essitentials are 4x4, a tide chart and a tow strap.