I'd tend to agree with the you've got all you need viewpoint but at a push I'd say Alive II ,Love Gun or the first S/t unless Double Platinum is also on offer
someone will mention Music From The Elder, ignore them it really is SHITE of the highest order
if you want some dumb 70s rock n roll on the cheap I'd recommend something other than KISS who whilst writing some canny tunes also had a lot of filler
edit useful suggestions
James Gang Live or Miami
Gues Who Live at the Paramount
Bachman Turner Overdrive Not Fragile/4 Wheel Drive
Allman bros Live at the Fillmore
early Ted Nugent
I see all the Grand Funk cds have been remastered too
Hah! Some tempting suggestions there actually. I did get a Grand Funk album a while back (the live one?) and wasn't that impressed.
Edit: actually, I've already got the Elder. Didn't mention it because I almost don't count it as a Kiss album!