The compact macro is a nice lens, and just like it's name implies... it's compact. The 100 macro drives me nuts... it's so big! The EF-S 60 macro is a real stunner and worth it. But the 50 macro is also quite good. I don't know what you are shooting, but often, many macro shots aren't at the full 1:1 magnification. The 50 compact macro gives you 1:2, which for many things, is quite adequate. But if your macro needs are for REAL closeups, then you'd probably be better served with 1:1 macro lens.
If you are on the cheap, then it's hard to go wrong with a set of extension tubes to bring macro focusing distances to your existing lenses. That is a cheap but effective way to go. You can also reverse a lens to get macro magnification, but you lose all the electrics, which to me, is not very nice.
Another cheap alternative is to buy a super cheap and old canon 35-80 lens. You remove the front element and it becomes a macro that gives you greater than 1:1 magnification. You lose focusing ability so you have to move your camera to achieve focus, but if you are always doing closeup work with it then it's a somewhat livable crutch.
All in all, I would probably go for the 50 compact macro. I LOVE my 60 macro, but I'd probably just get 50 if I had to do it all over again.