Ok, just hung up the phone. Here's an abbreviated version:
Me: hey, so what did you think when you saw the total on the bill before you faxed it over?
Him: [deep breath / sigh] I thought it was high. What did you think?
Me: Well, to be honest, I choked on my coffee. I thought it was real high, like double what i expected it to be.
Him: Yeah, i've been exptecting your phone call.
conversation goes on about how he had his guy sandblast, pressure wash, polish and gold plate every nut bolt and part....that it was like having a puzzle to put together (WTF? - isn't that what mechanics do?). bla bla bla, i took some time off and told my guy there was no way we could charge you that much, i cut my labor rate. i reiterate that i provided everything needed as soon as they asked for it, provided tech help when they needed it, manuals, diagrams, etc. The fact that this was a "get to it when you can" project that's been going on for 5 months, etc. etc.
Him: I understand, let me think about it over the weekend and we'll talk monday.
Me: I appreciate the work you guys did, it looks really good. I dont' want you to feel like I'm trying to beat you up or for you to lose money on my little toy project, but I can't help but feel this isn't reasonable. I hope we can find some middle ground on this and both walk away feeling good about it. Talk to you Monday.
End of conversation. It went as well as it could have i think. I'll report back Monday on result.