you can buy peel and stick vinyl tiles for under a buck a square foot if you just want to cover the concrete. you will have to buy a moisture barrier primer product to paint onto the floor before you stick them down.
they also make vinyl planks that "click" together like laminate wood flooring. its a floating floor, no adhesive (I suppose it makes it fully water proof as well). I believe that product is available starting about a buck a square foot. you cut them with a utility knife and go to town.
It's not bad stuff but it's a lot more than $2.50 a foot. As for water proof, if you get water under it(as with a flood) the water will become trapped beneath it and grow mold and or mildew which would be no bueno.