Before you make the purchase, you might want to look at the Genesis version, Contra Hard Corps.
I have only played the SNES version, so don't take my word as gospel, but some people are suggesting that the Genesis version is actually better than the SNES version. Apparently the only difference is that the Genesis version doesn't have (or changed) the top down levels.
This is what I have heard, so please don't take it as gospel. I haven't played the Genesis/Mega Drive version, and I don't think the PAL regions even got the Probotector version on the Mega Drive? I'm not a big Contra/Probotector fan, so I have little reason to invest time into researching either game.
Just thought I'd mention it. You'll probably want both versions anyway, making this message pretty mute and void, but at least I can say I "tried helping" a fellow collector.