This one isn't even worth discussing. No way can anyone do it for $500. I wouldn't letter it in die-cut for that unless like weasel said you're doing a 4' x 6' area on both sides or something. I could see getting beat up for a few hundred or maybe even a grand, but not for almost a 90% discount ?? Don't waste your time at all with the dead-beat.
I just had a guy today tell me he could get what I offered for a fraction of what I quoted him. I played along a little bit and looked at my quote, took out a pen and did some math [that I was just faking numbers], looked up in the air, wrote some more numbers down..... said to him, I'm working on something here. I told him that other deal sounds like a good deal to me. I'm trying to help you, please hold on a minute yet. He seemed happy as he was smiling.... until I said, yep, that's a really good deal. I can't even get the materials for that, so I'm sure you're getting some inferior materials and probably some shoddy work. I asked him where he got the quote... he told me and I said... Okay, now it makes sense. So I said.... I don't bad mouth competition, so if you want, you get it there and I'll be seeing ya around. I shook his hand and he said... can't you do a little better for me. I really want you to do the work. We're not talking the same stuff here, not at all. The other guy said he could put red 8mm neon around 2 windows 5' high and 10' long. That's 60 foot of glass and stuff for $400 total. I was quoting 13mm. He's gonna get a 4' x 6' double sided sign changed out for $265. That's a total of $625 to do the two windows and two faces... oh, plus letter the front door. The artwork has to be digitally printed because of all the effects he has on his art. I can't wait to see this in a few weeks.
Just stand your ground, smile and walk away.