Is it a Chinese 100 round drum? If so those sell for $250 to $300 themselves. The Chinese 75 rounders sell for a little less, probably around $200.
I wouldn't trade, being it would be a lot harder to get another mak 90 than a mini.
Is the Mak 90 the one with the slant cut receiver or a straight one? I think the straight ones go for a little more also.