Two Part Polyurethane Paint

I recently painted a concrete floor for a client with the paint he wanted. Now they want the word has been brilliant. Is a water-based polyurethane be used over painted concrete? It is a two-part epoxy shield that can be used but the client was not happy with the price, it ran about $ 60 for the kit. Suggestions?

Several layers of water based poly will run for a while. But like any poly, it must be sanded and applied also wear shows (like wood floors). In the order of things, $ 60 is not much to pay for a long life finish. epoxy finishes can stand much traffic and are more profitable than poly.
Hope this helps.