I posted my "halving every 18 months to every 2 years" guesstimation some time ago, and I remember specifically looking at pieds, het pieds, and lessers. Just to double check myself, I did it again. It took about 1 minute.
1) Do a search on the Ball Python section of fauna classifieds for 'piebald'
2) Pull up the first result (2011, very recent) and last result (2005, 6 years ago)
new
http://www.faunaclassifieds.com/foru...hlight=piebald
old
http://www.faunaclassifieds.com/foru...hlight=piebald
3) According to my estimation, if 6 years ago a piebald cost 6k, then today it would go for $375-$750
4) Recent post lists asking price at $600.