I'm also from Texas, but I see this entirely different than the OP does. 6.25% is a steal! Honestly, a lot of states have it worse. As was said earlier, I remember reading that CA has > 9% tax on cars and you get taxed on the entire purchase price, not the purchase price minus the trade-in value.
I always factor the 6.25% into the car value, which is why I had Tesla buy the car via trade-in after being adjusted for a Carmax quote. I wouldn't be able to get enough via private party to justify selling it myself.
Also to the OP, I don't understand how you are losing over $7k. If you had traded in your car to offset the price, you would have only saved 6.25% on the difference in trade-in value. Unless you were trading your model S in for $112,000, you would not have lost $7000.
If Tesla offered you $38,000 on your car, then their offer to you is in reality, $38,000 * 1.0625 = $40,375. As long as you sold the car for more than that, you're still coming out ahead. I think you're either misunderstanding our tax law, or did some extremely funky math.
I personally have no problem paying sales tax on a new car. It's a lot of money, but Texas does it right, imo (as do other states). Normally sales tax is a regressive tax in that it hits lower income families disproportionately. They negate this by making food and basic necessities exempt from sales tax. A new Tesla is far from a necessity and absolutely a luxury. I'm more than happy to pay the tax that is used to fund the state's programs.
As was mentioned earlier, you need to absolutely take into account sales tax when figuring total cost of ownership (as well as maintenance, [PPF, ceramic coat
] and anything else that you add to the car).
At the very least, recalculate how much money you "lost" in sales tax so that you'll make yourself feel a whole lot better. You probably lost something closer to $3k, though I have no idea what you sold you car for.