I understand the financial part of wanting the shirt chewing to stop but putting something on a kids shirt that tastes bad to prevent them from doing something that helps them to regulate is just cruel. Its like slapping their hands for flapping or stimming (which is what the chewing is btw)....they are kids, not dogs...I wouldnt even do that to my dog. Id give him something else to chew on. Sorry if I come off as a little harsh but think about what your doing.
I saw this thing in a kids magazine once, it was a plastic cover for their thumb to keep them from thumb sucking....to me it was just hideous!
I like the idea of the sweat band things to chew on...thats a good idea or try the chewease with the cloth covers....or go to wally world and get some cheap wash rags and let him take those to school with him. There are several other ideas Im sure you could come up with. Hes old enough that you can reason with him to use something other than his shirt to chew on. OK, Ill shut up now!