So when I did my basement floor (very similar to a garage floor slab) I first cleaned it with a warm water and hydrogen peroxide mix, and then a water and TSP mix. I sealed the whole thing with 3 coats of Kilz, let that dry for about 2-3 days, then applied some Behr paint for garage floor.
It's holding up okay but is not easily washable. I have to scrub like a crazy person to get dirt and stains up. Overall, that probably cost me around $90 and it looks 10x better. I know they make kits out there specifically for garage and basement floors, but they run about $150 and you generally need to do an acid wash first.