E-Auctions-Express via eBay offers the Merax Total Body Ab Workout Machine for $39.60 with free shipping. (
Meritline offers it for about the same price via coupon code "MLCF27FA".) That's $20 off list and the lowest total price we could find. It features adjustable dual resistance ranging from 24 lbs. to 48 lbs. and an assist function.