Last year I bought two of these Sigma BC 5.12 computers on EBay for about $18 each. It is easy to install and easy to read while riding. It shows just about everything you would want to see, and can be removed from the handlebars with just a twist. There is no backlight, so if that is something you need, check out the BC 16.12.
This is the 5.12 model. Sigma has a very good website.
