Come up with household items which you can use for your PSK, then have the scouts and parents collect them. Altoids tins, breast milk bags for water, compact discs for mirrors, string, etc. This will also teach resourcefulness in utilizing commonly found items for survival.
You must also base your kit on the proper priorities. Maintaining body temperature, water, signaling. Younger scouts need to worry about staying alive until found and getting found. Your costs can be reduced with the proper prioritization. I like Jim's suggestion, buy them all a heat sheet to keep in their pocket. Probably the most efficient and effective (and versatile) thing you can get them.
I have my scouts carry a light, whistle, heat sheet and bottle of water. They are taught to stop, remain safe, and get noticed. As they get older, and their adventures are in more remote areas, their needs will change. If they have done the wilderness survival merit badge training, they have a good base of knowledge. The older ones have also had more time to pull together the items for their kits. I do not think you can get a good one together for $5 though.