Surprise bill on Project?

[skigoose]

I am just asking the opinion of you guys out there.

The shop working on my car ( and they are doing good work) gave me a quote to assemble my 68 Charger with all the parts I supplied them, they came out 3 times to check parts and est. the job, well we are coming down the home stretch, and all of a sudden they are saying it is gonna take another 50 hours of work..Keep in mind I understand that this is Kinda a custom build, but nothing that they have done was not in the scope of the project est. if anything was needed in addition to what I supplied, I paid them for it right away, now it seems that I have made my final payment and my car is on the back burner in the shop. The owner asked if I would split the hours with him, because of the surprise, but I am having a problem with accepting that

Any suggestions??