Texas has a cost of living index of 94 relative to the US average of 100. This is close to the national average. Texas offers a typical cost structure — housing and expenses track closely to US median.
The 4% safe withdrawal rule suggests a FIRE number of 25x annual expenses. At Texas's median income of $67,700, that is $1,692,500. However, if you plan to spend more (or less) than median income in retirement, scale the number accordingly.
Texas has no state income tax. Roth conversions, capital gains distributions, and IRA withdrawals all avoid state tax in TX. This makes Texas one of the most FIRE-friendly states from a tax perspective.