You can use fairly cheap substitutes: My preferred one is the very same old inner tube, cut to fit. Cut a stripe a bit wider than the rim, and it's lenght should allow to go completely around the rim. Use patching glue to close the loop. the loop should be tight enough so it keeps in place by it's own tension. To properly glue the ends of the rubber, use sand paper to buff the ends of the stripe and use more glue than normally used for patching. Apply glue to both ends, allow to touch-dry then press ends together and let sit 10 or 20 minutes before installing. Do not forget to cut a small hole for the valve stem. The stripe should have one side completely facing out (no twating!). These expensive "Inner Tube Protectors" have served me way more years than the tires in all my mountain bikes, wich I ride at 45psi aprox.
Medical adhesive tape (the cloth-like variety) is also very suitable and affordable and easy to use, but I have never used it personally (Friends of mine use and recommend it too).
Vinil used in advertising banners can be used too, but some varietys (most, actually) are not stretchy so the ends of the stripe must be glued while already in the rim. Vinil can be glued with rubber cement.
Many kinds of cloth can be used, they must be like painter's canvas, soft denim, the kind of nylon used in back-packs. These can be also glued with rubber cement. Stretchy cloth can also be sewn with a soft thread.
For emergencies many kinds of tape can be used, like electrical tape, masking tape, etc. As long as it is soft enough to adapt to the rim's well and not have a sharp edge or wire reinforcement, etc... However, these solutions often are not long lasting as for example Masking tape is paper-like so it practically disolves on water, electrical tape adhesive sooner or later degrades to a messi, sticky useless substance that will make a hassle every time you have to patch or replace tube/tire.
Moneywise anecdote: On a local store inner tube cost the equivalent to $7.5 and the rim tape $40.00 (they only had fancy stuff). The old tube I was about to replace had cost $4.0 and it had enough rubber for 3 "Inner Tube Protectors". I just needed patch glue, sand paper and scissors.