From yhe TPWD website - The single Texas State Park Pass (Primary Pass) may be purchased for $70. An additional (secondary) pass may be purchased for $25. Primary and Secondary pass holders must reside at the same address.
•Veterans of the US Armed Services holding a 60% or more service connected disability, as determined by the US Veterans Administration, or loss of a lower extremity. US Veterans meeting these eligibility criteria will receive a 100% discount on entry fees to state parks where entrance fees are collected.