I was given some precious information from Carrie Koffman when I studied with her at Boston University. She knew that me, like all music students, could use a few "hacks" when it comes to overpriced materials.
1. Mouthpiece patches made of medical tape
Instead of buying mouthpiece patches, use rubberized medical tape. The key is buying medical tape with rubber that can handle moisture (not just paper, which will be useless). A spool of this magic lasts me a few years and costs less than $3.
2. Teeth guards
In addition to the malleable thin plastic that is boiled and then molded to the mouth, teeth guards can range from folded band-aids to slips of paper. Ezo denture pads in "lower heavy" are my favorite lower lip guard. These handy little pieces of wax protect your bottom teeth from callusing your bottom lip, which is especially useful for those who have braces. One package cut up into half-inch pieces is worth its weight in gold.