If you're okay with a platform look, few things are cheaper than a 2x6 on edge (5.5" nominal width). This was (is?) a standard way to get cabinets up off the floor in schools and institutions. You could miter cut the corners and give it a coat of paint, or just cover it in vinyl baseboard trim. Short lengths (rather than rolls) with a peel and stick backing are available at most box stores inexpensively.