Warning, I've never used interchange, only heard of it.

Oscommerce seems to have a lot more "mindshare" in this arena. (but that's php). Seems to work okay. If you google around renacoder/elance, you'll find a lot more references to oscommerce than any perl shopping carts, I think.

If this were my project I'd probably go with oscommerce cause of the mindshare, even though I like perl better, but maybe I'm just a weenie.