PVC pipe, but unless you can find a scrap piece the right size it's probably going to cost you more than the trays. The new ones are very sturdy, not like the older really thin ones.
I’ve had so many of those nice stainless steel or PVC trays stolen over the years that now we use a gallon windshield washer jug with part of the side cut out and about an inch of the top cut off so it will fit into the coin vault. It works fine.