Thanks for the leads.
Regarding what I'll pay- it depends what you're selling. A set of aftermarket lightweight forged pistons are not the same as a set of stock BMW pistons. I'd think that if new aftermarket pistons can be had for $175 each that used ones should be less than $100 each depending on manufacturer and condition.Like anything there is a bid side and an offer side. often the difference between the two is quite wide. When you go and sell your gold to the jeweler you're likely selling it at a 20% discount to spot. This is the jewelers profit margin. I'm not looking to "steal" a set of pistons but I've found that I often have parts sitting in my garage that I don't need that can be turned into cash while at the same time helping a fellow BMW enthusiast.
I'd like to hear anyone else s opinion as to value..