Sheet vinyl or carpet. The "nothing expensive" is going to be a problem because garage slabs are often slanted (so that water runs OUT of the space to the street) and they are without the vapour barrier that all "living space" slabs use (recent builds anyways).

So....to remedy these two issues will cost a small fortune. The way around both would be to work with flexible sheet or roll material....such as vinyl or carpet.

Polished concrete is also another way to go. And just a little FYI...the only two floors that will survive a flood = concrete and porcelain. Everything else will need repair/replacement.

A properly installed "loose lay" vinyl plank might work. It depends on how much of the slant you got rid of before you finished the space. But you still need a vapour barrier because of the garage slab itself will cause moisture to build up underneath the vinyl causing BIG problems down the line.