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.

I have used the lid from a plastic box (after the box was broken). Tub surround scraps from a remodel. Roll up kitchen cutting mats. plastic from bacon package. About anything washable will work, and it saves putting so much in landfill.

You could use an old cutting mat, or plastic placemats as CarrieC suggested.

The minute the elections are over, I help the canidates by removing signs made of corigated plastic. They work great and can be cut to size with an exacto knife.

I do call the canidate for an ok, as they may want to reuse the signs for their next run. Save a few signs, on the wires, makes a great base for yard sale signs.

I use thin sunglasses from Lowes, Home depot, etc...they will make one or two cuts for free and you can also cut at home. Make a 'sleeve' to cover and slip it in. Works well and no bending or folding!

In a pinch I have used milk cartons, cat food containers, large washing detergent, etc.(washed/plastic) for the bottome of round item or small items. Some fit perfect.

I found some plastic placemats at the Dollar Store that were thicker than most plastics and made the bottoms for 2 Bow Tuck purses so that came to $0.50 each. I always make them so they are removable. I simply make a sleeve to fit and sew it closed. I find the stiffer bottom doesn't need to be washed very often.
Sue

Dollar store cutting mat??? The plastic back from a school notebook ??

I have used the boards from old clipboards. They are very sturdy. I just measure the size I need and then cut it with a jigsaw.

Cute purse. I use two pieces of fusible timtex. I fuse the two pieces tpgether and when the outer portion of the purse is completed, I will fuse the timtex into the bottom. This way the bottom is very sturdy and very washable. I have no problem with it getting soft and bending with two layers.