"...cpr masks were quite expensive..."
If you go to your local ambulance company/fire station/law enforcement agency, in uniform would help, and explain what you are doing, you MIGHT have some supplies donated. Maybe. Before I retired I was the supply guy for that kind of thing, and I would have slipped you some stuff under the table...
Yeah - you'd be surprized how people will go out of their way to help. I've found the uniformed guys are typically more than willing to help out any "real" volunteer group - Boy Scouts, Girl Scouts, Heck, even SOME Ham radio operators. Hint, when I spent 12 hours with my truck parked behind the Red Cross ERV, and even took over when the ERV went to refuel, the police noticed I was serious - and they usually look down on us. Before I left, a case of flares was dropped in the bed of my truck to "replace what you used"