How much would you spend on a used AL80?

[mud_diver]

This board may be a little different, but I recall reading someplace that the average diver will dive 6 times per year.  5 free air fills, assuming the shop fills if the first time is $25 using your price for air.  That cost, on top of the $149 or whatever a shop typically charges, is still less than $190.  Now if you dive a lot, roughly 38 times, on air, with that same 80, the tank is "free".    Still not a good deal
Edited to include that all of the fills need to come from the place you bought the tank, so dives done with the tank on trips are still costing you for air fills.

In that case, I am not an average diver. Nor are any of the scuba divers that I know. Most, if not all, of the divers I know, will exceed 38 dives a year. If you are going to dive only 6 times a year, you might as well rent your gear.
Also that is why I bought my tank at the closest shop to my house, so I could always fill my tank there whenever I pass by.