I haven't seen it and I'll give $40.'
I'm pretty confused by the measuremets 6' x 24" cylinder? 6 feet tall 2' diameter? 2' tall 6' diameter?
Honestly it's really hard to give you any idea on price without a lot more info. Does it come with a stand, canopy, lights, skimmer, reactor, sump, etc? Condition is everything. A pic would really help. Many people on this site that would probably be interested. I would guess it could go anywhere from $200 - $2,000