As KDTX said....

"our hourly rate is (fill in blank). By the looks of what is needed, I will need at least (fill in blank) hours with your bike"

I also add in the following statement "Thats for labor only, not including parts"

I do exactly that when I see a bike that looks like a real headache waiting to happen. I'm a small one man repair shop and I have more business than I can handle so I'm ok with using the above method to politely turn people away. I've also quoted people a 3 week backlog on repairs when I only had a two or three day backlog.