Texas also has a state sales tax for aircraft bought in state and a "Use Tax" for aircraft bought out of state, and it's pretty hefty at 6.25% for the state and up to an additional 2% for local (city/county/district/etc) tax on top of that for a possible 8.25%.
However, there is an "occasional sale exemption" that may apply if you buy an aircraft from an individual who does not "habitually engage in the sale of taxable items" and has not sold more than two "taxable items" during a 12-month period. Neither buyer not seller can hold a sales tax permit at all, from Texas or any other state, even for completely unrelated business. For example: if Billybob makes and sells homemade fiddle bows out of his workshop, has a tax permit for that, and sells his RV-4 to his cousin Earl who also lives in Texas, now Earl must pay tax on the sale, but if Billybob didn't hold a sales tax permit for his small business, Clint would've been exempt from the tax. Also if the buyer, Clint, was the one with a tax permit for his small home business, and the seller Billybob didn't hold such a permit, then Clint would also still be required to pay tax.
So, in Texas, if you want to buy an aircraft, don't hold a sales tax permit for Texas or similar permit for any other state, and buy the aircraft from someone who also does not hold a tax permit for Texas or any other state, and you may qualify for the occasional sale exemption.