Build me a basic bar code scan app for DROIDS

I need a pretty basic app that does the following: Ability to scan bar codes, the ones you find on your Cocacola can for example. When I scan a bar code I want it to tell me a message. The messages are set when I first scan a bar code -- so the scanner would tell me the bar code message does not exist yet and that one needs to be set. Sorry if I explained this badly, but it is very simple. I have a very small budget for this so hopefully it is as simple as I think.