As weird as it sounds, the Turbo/PCE was always my "budget" system. I don't think I've ever paid more than $30~$40 for any Turbo/PCE game, nor have I ever bought a stand-alone, brand new retail game for PCE/TG (other than Insanity).
It just somehow worked out that way for this particular system. I only really got into the system during its deathbed years (92-93 or so?), when things were going off on clearance. (I remember getting games like LoT, Exhile 2, and Spriggan, though a bit scratched, for <$5 off Game Dude in Hollywood). I then acquired most of my PCE collection dirt cheap in Japan during the time I was living there.
But for other systems I can recall:
New Import - $90 or so for a new, MD Valis III
New Domestic - $70 (or was it $80?...) for Phantasy Star II
Used - $170 for Phantasy Star Gaiden (*ouch* -- back when demand for PS series seemed to be at an all time high, just around the release of PSO)