Hasselblad A24 back for sale, for use with 220 films (and no, I have no idea of whether it will work with 120 -- my bet is that it won't, but I have never tried it). Works fine but it ain't pretty -- probably a 6 or 7 out of 10 cosmetically, but the dark slide is in good condition and it hasn't ever produced overlapping frames or jammed on me.

$40 plus shipping