If you're handy with a needle and thread, you can make your own slip cover using fabric you have lying around the house or an old set of sheets. You can also find inexpensive fabric at craft and fabric stores if you plan ahead and watch for sales. Use an online tutorial with step-by-step instructions like the one at allfreecrafts.com. Making your own slipcover takes a lot of time and patience, but the finished product can save you a considerable amount of money.
If you're all thumbs when it comes to sewing, you can also fashion a no-sew slipcover with fabric or old sheets and tacks. Make sure you have enough fabric to cover the entire area. You can use joann.com's free online tool to estimate how much fabric you will need. Use a staple gun or upholstery tacks to secure the fabric–both can be found at hardware stores.
If your sofa is showing wear in a few specific place–like the arms and back, you can use doilies, throws, and pillows to cover those worn areas as if they never existed. You can find inexpensive throws and pillows at the discount stores for as little as $10. Choose one or two throws that complement the colors and pattern of your sofa. Drape one over the back of the chair or sofa if that area is showing wear, and place one or two over the arm if one or both of the arms is showing wear. You can even use cloth place mats, pretty cloth napkins or a table runner to cover worn areas. Lastly, tuck pretty, eye-catching pillows into corners to draw the eye away from worn spots.