There are lots of garage floor coverings you can consider, both to give a little color to the space and to protect the floor from stains, road salts, and moisture.
The most affordable option is simple concrete floor paint. This is a tougher version of wall paint, and all you do is roll it on as with any other type of paint. The downside is that paint isn’t as good for protecting your floor as other coating options.
If you do choose concrete floor paint, you can select from latex or oil-based, with latex being easier to apply and clean up. Latex dries to a low-sheen flat finish (oil gives you a high gloss).
The cost runs 15 cents or less per square foot for one coat, and you can pick floor paint up at any home improvement store.