What I do (among other things used) is take a school binder and cut the cardboard to 1/2" shorter on length and width of the purse bottom. The cardboard is covered in vinyl. I then cover with the fabric I use for the inside. I do not insert this so it is permanent in the purse. I leave one end of the bottom inside of the purse 'open' so that I can slip the vinyl covered cardboard in and out of the purse when washing. Not all of my patterns have a separate layer of fabric in the bottom for inserting this, so I add the layer before sewing all the bottom seams. One short side is hemmed under and that is the side the cardboard/plastic/acrylic slides in and out of. I get the binders for .99 sometimes and I can get from 2-4 inserts out of them depending on the size of the purse.