Ask HN: Exploiting the "group buy" to finance new products

I'm talking to Hyperco about making a custom front spring for BMWs. Setup for the CNC machine is about $600, and I can get a per-piece price of about $30 if I buy 200 pieces. I figure I can sell them for $120 a pair. All I need are a few customers...

The obvious place to find customers for suspension upgrades is in BMW forums; but most of the forum owners want $200+ before they'll allow me to determine interest level. Call me cheap, but up front cash doesn't appeal to my scrappy nature. I want to test the product idea before putting up cash.

WePay and Twitter are both great tools for this kind of situation, but my problem is targeting buyers who aren't being protected from predatory entrepreneurs like me. Are there "group buy" web sites that invite my kind of society? And, if you think I should just pay the $200, let me know. Maybe I really do need to buy those first few customers.