From what I have seen you can have them made pretty cheap. I use a promotional shop that does stickers, shirts, business cards and such, they have a guy that specializes in stickers.
My Girlfriend is into this scrap-booking thing and she has this machine called a cricket. She used it to make me new lettering, she said this thing will do just about anything you would ever want.
Local sign shop is the way to go. One big benefit is you can work with the people at the shop to help design something cool. If you buy online or from a boat shop, you don't have the opportunity to look at a few examples or options.
