I haven't bought one yet, but Baby Co had nice looking nappy bags that were really cheap, like $25 or something. They also had larger ones that fold out and can store a heap of stuff, they were more expensive but still under $100.

I don't know what brand they were, and they weren't patent leather or anything, but they looked good to me. Then again, I haven't had any actual hands on experience with nappy bags so please correct me if you know otherwise (please do, or I'll probably end up buying one of these bags).