I gather some of the A-100's modules are quite similar to the Korg MS-20, most notably the A-106-1 filter and the A-119 envelope follower. When trying to exactly match all the things a particular hardwired monosynth can offer, you need to get a fair few modules, but then you end up with something *much* more flexible than what you were trying to emulate. For that budget, though, you'd probably want something a bit more basic to begin with. Then, as you'd expect, there'd be some things the MS-20 can do that this particular A-100 can't, and vice versa. (With only one A-106-1, for instance, my highpass and lowpass filter have to share a single cutoff point, which suits me just fine. And having 1V/Oct for the A-100's oscillators is much more convenient for me!)

And once you start looking at things like the A-127, you can forget the MS-20, you're starting to get into PS-3300 territory... :D