I have used home made potty pans before. Their made from Glad Disposable plastic containers(largest size quart container they make). Their nice cause if you have that fussy hamster which prefers their potty be completely enclosed you just snap on the lid, for that hamster who prefers openness you leave off the lid. For a box of I think it is 6 containers your only spending +/- $4.00 and you have multiple potties.
These pics are of my 1st attempt so they are rough and not perfect. I used a sharp tile knife to start the opening, then used scissors to cut the opening bigger. Today I would most likely use a hot blade or a Dremel to make the opening much much cleaner so it was nicer looking(though the hamsters never minded the crumby look of the hole)
However these few photos will help with the idea of how to make a inexpensive potty.
Home Made Potty pan-a.JPG
Home Made Potty pan-b.JPG
Home Made Potty pan-c.JPG
The pic had Wood shavings in it but they work much much better using sand. If you have that vigorous digger, you can make the side opening higher so the pan is deeper. If you wanted a heavier duty potty you can do this with a Tupperware container or any smaller storage container too.