Easy, don't let your newbie crafters use the expensive stuff until you trust their abilities.
And honestly, GMH's should be looking for talented crafters, not people who are going to waste their resources.
Having them use the cheap stuff is still a lot of cheap stuff, though in my example Salarr crafter needs hides to practice tanning. Takes a lot of hides before they're getting good at it and don't ruin them. 50 tandu/gortok hides is till 50 hides that need to be collected.
Point me to one crafter that skilled up BEFORE going to a GMH. That was the only reason I, as a crafter, would ever have gone to a GHM. I get the resources to work at my craft, I get protection, I get food, I get a place to sleep, and I get(hopefully) PCs with knowledge to share with me. Without PC hunters in the clan, getting resources can be difficult.
I've been a PC merchant in Salarr without any active hunters and 1 or 2 crafters. Trying to get resources is HARD. They can't just go out and start hunting goudra and tandu. Sure, they can go forage for branches and stone, but that's about it. It shouldn't be hard for a GMH to get resources, and it -seems- like it is now. Again, speaking from past experience and maybe all those indi hunters are actually able to help out and get what is needed.
I dunno, maybe I'm the crazy player that LIKES sitting around an RPing crafting and making things and getting them to people and organizing the crafters hall and making sure we had the right supplies and making sure my hunters were properly outfitted. I loved the merchant role, even if it was more often than not a PC shop. :-D
Also, I don't know how long you think it takes to clean up some place, but I've knocked out an entire compound in 3-4 hours.