Cathy is telling you the "money" end of it, but there's more to it than that. Although Singer did make them by the millions, that was generations ago. They are no longer made and are a finite commodity. Prices vary by region and availability. For instance in Springfield, IL you can't find treadles. Most of mine came from elsewhere.
If you have all the parts it's worth refurbishing. If you don't want to do the work yourself, at least give/sell it to someone who will. Don't let someone destroy it by turning into a table.
Joe