Some of this depends on what you are getting from them. A basic stage III body/chassis or what? They may be very buisy and trying to schedule etc ( if they have/practice a good buisness model) and need for you to commit and hopefully to them keep your mind off desertion. This helps them deliver consitently to all their customers.

If they deliver things on schedule, which I am very scheptical of in general, and they are doing a more complete build especially, they have to invest time and money up front to have parts (long lead items) ready to go to deliver your job on schedule. Naturally that costs $. The bigger/more established the outfit is the less this is critical to them.

Bottom line from me is that for a stage III body/chassis turnkey and above I would expect to pay up to 50% up front.

I see many outfits with various, attractive pay as you go programs. However no large amount of time you spend on investigation of them will be too much.

Good Luck, Kitz