I totally agree with all the posts like this.
$6000 is total BS, and CA law does not allow them to keep your car.
Personally it makes me wonder what you have already paid this guy for.
For 6 grand I'd fly out there, buy the tools new, do it for you in two days and take the rest of the month off.
(and STILL come out pretty good on it.)
It's not your financial responsibility to train this guy on how to do something he lead you to believe he was capable of doing.
4-600 I could see.