As far as bumper stickers go, it is an expensive proposition if you don't get a large quantity. I'm sure there are lots of companies offering low prices and low quantities but my experience has been that most of those end up being not what you expected.
The importance of an experienced printer can't be overstressed here. There is so much to consider; the adhesive. the material you are printing on, the type of ink and complexity of the design, etc...
If you have any specific questions, email me and I will help you.