I don't know of any 100 round AK drums...never heard of one. I have a romanian 75 round one that I bought for $75. That was a few years back...ever since I've seen them at gunshows for twice that much or more.
I also had to modify my rifle a bit so it would fit, they did a crappy job of cutting out a single stack receiver into a double stack, which didn't suprise me (CAI is known for...iffy...quality control). My WASR-10 would fit most normal double stack magazines, but it wouldn't fit the bulgarian polymer magazines or the romanian drum without some heavy file work.
Loading it is a pain, but I prefer the romanian (I hear it's identical to the russian drums, which are apparently unavailable here) over the chinese style. And I hear it's fairly easy to accidently damage the chinese drums...
Oh and keep in mind that fully loaded, it weighs more than your rifle. Mine is a fun novelty, but lets just say I don't keep it in for home defense purposes...it's more of an investment/toy/SHTF thing.
-Jonathan