I use the largest sized throw away aluminum baking pan I can find in the store. They last quite a long time and are less expensive than conventional litter pans of any make. When it gets beat up enough that I have to get another, I just take it to the scrappers when I take my aluminum cans in.
I am fortunate in that I live in Florida, where it is usually warm enough, and we live in the woods w/o close neighbors, so my two adults are savvy enough that they come and go in and out during the day as they wish. The two little 'teenagers' are learning the ropes, as it were. So they are outside most of the afternoon, but I still get them in at night.
The litter pan is doing double-duty right now, with the two new kids, and the cold weather that NE Florida has been having. But this should abate some once the weather gets (and STAYS) better, and the kids grow up.
The two kids are now 5 months old, perhaps 6, (both are boys) and are starting to wander, so they are going to get a rather unpleasant visit to the vet at 8:00 AM Monday morning...
Please keep us in your prayers and wish us well....