Mulch it with whatever you can get your hands on and that is cheap......wood chips (often free from utility companies or tree services), pine needles or even straw. All should help keep the yard mud-free and will keep down the weeds but they must be applied thickly enough to be effective....2-3 inches.

If you want some sort of color, plant up some containers with seeds or any annuals/veggies available at groceries or box stores if nurseries in your area are not open.