From what I'm understanding, the mechanic did the work but it was far above the initial estimate and you were allowed to remove your car from the mechanic's shop.
Technically, since you stopped payment on the check, this brings about the mechanic's rights to repossess the vehicle and hold it until you pay the rest of the amount due. The law providing this is as follows:
Sec. 70.001. WORKER'S LIEN. (a) A worker in this state who by labor repairs an article, including a vehicle, motorboat, vessel, or outboard motor, may retain possession of the article until:
(1) the amount due under the contract
for the repairs is paid; or
(2) if no amount is specified by contract, the reasonable and usual compensation is paid.
(b) If a worker relinquishes possession of a motor vehicle, motorboat, vessel, or outboard motor in return for a check, money order, or a credit card transaction on which payment is stopped, has been dishonored because of insufficient funds, no funds or because the drawer or maker of the order or the credit card holder has no account or the account upon which it was drawn or the credit card account has been closed, the lien provided by this section continues to exist and the worker is entitled to possession of the vehicle, motorboat, vessel, or outboard motor until the amount due is paid, unless the vehicle, motorboat, vessel, or outboard motor is possessed by a person who became a bona fide purchaser of the vehicle after a stop payment order was made. A person entitled to possession of property under this subsection is entitled to take possession thereof in accordance with the provisions of Section 9.609, Business & Commerce Code.
(c) A worker may take possession of an article under Subsection (b) only if the person obligated under the repair contract has signed a notice stating that the article may be subject to repossession under this section. A notice under this subsection must be:
(1) separate from the written repair contract; or
(2) printed on the written repair contract, credit agreement, or other document in type that is boldfaced, capitalized, underlined, or otherwise set out from surrounding written material so as to be conspicuous with a separate signature line.
(d) A worker who takes possession of an article under Subsection (b) may require a person obligated under the repair contract to pay the costs of repossession as a condition of reclaiming the article only to the extent of the reasonable fair market value of the services required to take possession of the article. For the purpose of this subsection, charges represent the fair market value of the services required to take possession of an article if the charges represent the actual cost incurred by the worker in taking possession of the article.
(e) A worker may not transfer to a third party, and a person who performs repossession services may not accept, a check, money order, or credit card transaction that is received as payment for repair of an article and that is returned to the worker because of insufficient funds or no funds, because the drawer or maker of the check or money order or the credit card holder has no account, or because the account on which the check or money order is drawn or the credit card account has been closed.
(f) A person commits an offense if the person transfers or accepts a check, money order, or credit card transaction in violation of Subsection (e). An offense under this subsection is a Class B misdemeanor
(g) A motor vehicle that is repossessed under this section shall be promptly delivered to the location where the repair was performed or a vehicle storage facility licensed under Chapter 2303, Occupations Code . The motor vehicle must remain at the repair location or a licensed vehicle storage facility at all times until the motor vehicle is lawfully returned to the motor vehicle's owner or a lienholder or is disposed of as provided by this subchapter.
The best thing you can do in this circumstance is try to work out a deal with the mechanic. He should not have exceeded the estimate without first calling you and asking for your authorization. Thus, you have a legitimate dispute with him. However, if his charges are justified, then he has a right to get paid which will trigger the repossession lien stated above in the statute.
If he does not want to compromise, I would recommend paying him but sending him a letter stating that you are paying "under protest". Then sue him in small claims
court for overcharging you and breaching his contract.
Please let me know if this answers your question.
Zachary D. Norris