While most 8-bit games went to $1 at some time in the 90s and then some rocketed towards a grand by 2015, Drac X never did this. When importers started carrying it in 1993 or whenever, it was $70-100. It has pretty much kept pace with inflation since then.
It's never hard to find. Never cheep, but it shouldn't be expensive either. It's not rare in the slightest, but it is the most widely popular and highly regarded game on PCE so once you have it most of the other good stuff is cheaper.