You have questions that involve both Texas and Oklahoma law. Under Texas law, a car repairman would have a possessory lien against the car, and could hold the car until paid. I have no idea about Oklahoma law.
You write that a "person took car but never paid for car." If that means that they stole it, then you can initiate criminal prosecution. If you sold it, and the person has not paid for it, then you have a civil matter. That means that you can sue in a Texas court assuming that the sale occurred in Texas.
The Oklahoma mechanic may have done you a favor. You know where the car is, and to rescue it, all you have to do is pay for the repairs. If the car needed the repairs then you pay for them, and retrieve the car. Who knows where the person who took the car would have ended up if it had not broken down. If the car did not need repairs, then you have a whole other issue.
Bottom line: Go pay for the repairs and retrieve your car, and be thankful that that is all that it has cost you.