that is, $15 and up to maybe $20. all in good shape; quallity indicators include good siz magnet, vented magnet, cast metal frame (of which I have none), shielded magnet (if required).....
also check the 10" no name pair for $10. cheap but good starters or project subs.........
disclaimer! some might have sold.
note! there are a lot of cheap subwoofers out there, I know. some of these are from brand name manufacturers like energy, infinity, et. al.......