Same position here. Keeping the rate static would keep me as a customer, but huge increases force me to look at alternatives.

There’s a lot of shopping carts out there, but most do far more than Americart and want to run the entire web site. I like using Americart simply for letting people check out, and I prefer to keep control over my pages. The only tempting alternative I’ve seen is romancart, which unfortunately didn’t have a couple of shipping options we need. They’re based in the UK, seem pretty sensible overall, but like Americart they don’t seem to have enough staff to really be proactive about developing the product. MUCH cheaper, though.