Umm, Wikipedia just mentions two basic types of GC, a reachability based one and a reference counting based one, and I mentioned both methods without knowing a thing about GC. Same for the "What the heck is: Garbage Collection" article mentioned in the comment above, and the book doesn't seem to mention anything fundamentally different either, just goes into details (same ideas, different algorithms, though interesting ones. Especially the copying one is smart, as it solves the fragmentation problem). Isn't there another paradigm of doing GC out there? Or is the little I know really all that's to know about GC on a high level?
I was totally wrong on the overhead/cost though. ;-)