Is it a running team of survivors or is each game a one shot then new start on each play?
although the original is likely to be the easiest to get hold of cheap be aware that the newer ones have plastic player trays that make the game much less frustrating (I only have original and black plague so not 100% sure when it started). in the original you place card markers on top of a sheet of card for your upgrades during the game and a slight table knock moves them. not the biggest issue but the player trays added later are so much better.