A 1/5 HP chiller will work well on a 75g tank... but do you even need one?
As for reliability, provided it was well taken care of, not allowed to freeze, and kept clean, you can expect maybe 10 solid years, possibly as many as 20, depending on how hard it was run. If it only ran a couple months out of the year, it should be fine.
Honestly for an 11 year old chiller (if it's got 11 years of use out of it), I think 250 is a little steep. If it was a 2 or 3 year old machine, that would be a reasonable price.