Sourcing only your own materials is a good call for anyone to consider.
Someone else bringing in materials has to understand that sometimes cuts do not work right (do not bring in a priceless heirloom or sentimental artifact and just “hope it works out”)
They have to understand what materials are safe to cut (Not going to put it past them to bring in an object which appears to be solid wood, but is a thin case around some harmful crap)
They have to bring in a spare to figure out power/speed settings (how many people will throw a huge fit when you tell them to bring in 4 times the material they need - One to get settings, one for alignment mistakes, and one for the inevitable personal change of desired outcome or repeated mistakes?)
Personally, I won’t be charging anything at all, since mine is in a classroom. So either you look at it as I personally don’t charge them, or you look at it as the University doesn’t charge them more than other students who do not get to have time on my laser. Sure, they pay to be here (and that sucks), but not to use the fancy toys I try to provide.