Over $6000 to install TTI headers on 66 Barracuda

The mechanic who has done most of the work on my car and friends is charging me over $6000 for the install of TTI headers on my 66 barracuda The sad part, the work is not completed. He called and asked for a payment.
We had discussed the work and budget of about $1000 for the install. ( I talked to a different mechanic who stated it would be about a day and ½ of work, about $1000) When I talked to him he stated it was hard and time consuming and would go over budget. Which was raised and I told him my max.
He continued to having problems with the install and wanted to change out the motor mounts (which are 2000 miles old) and other work. At this stage, the headers are not even connected to the exhaust. And he is at 60 man hours. This seems crazy to me. Am I wrong?
It looks like I have little recourse but to pay, to get my car back.
Is there anything I can do? The better business bureau doesn’t seem like much help
And yes, I will be pulling my uncompleted car out of there. I have lost faith in mechanics and I am really down on the car now, which I am now thinking of selling. This is turning into a nightmare of a experience