That's right, the once sort-of-hard-to-find Metal Slug X for ps1 has had a new print run. I got a copy tonight at my local Gamestop for $19.99 new! It's available so far at Gamestop and Amazon.
You can't lose, a friend and I beat it tonight (yes, it's on the short side, but we used a helluva lot of continues :/) and it's a truly fantastic game! Who knows how long these will last, get it while the getting's good!
(sorry for the excessive excitement, I've just been searching for this game a LONG time outside of ebay with no results ).
Source: gamefaqs, gamestop