I have used vinyl siding. Find a house where the siding is being replaced and most workman are happy to have you pick up the scraps. I round the corners after I cut the size I need and cover with the purse or tote bag fabric.

Check out the product called Soft and Stable. I love it for bags.

I love using Soft & Stable, for all my purses now. However, I just made several 6- Pocket Hipsters, were I used a double sided fusible called Inn Control Plus. These two products are almost identical......and "dreams" to sew with.They are the same cost, and both are available in white or black.The end product is truly enhanced when you use either of these products

I like Timex.

You're my kind of person. I love using scraps and leftovers, just to make less waste in this world. We need to think about how much waste we make. I just had my 100 year old garage re-roofed with metal. I told the workers (Amish) to use whatever color they had left over from other jobs. The front needed to be sort of matched, but the back could be anything. They did a beautiful job. Looks like a jelly roll quilt! ! !

I also use car headliner as the stabilizer for the side of my bags. I recently found a light weight wood at the craft store. Thought, it covered with, fabric would be great for the bottom. Hubby also suggested an aluminum or Fiberglas ( such as the above mentioned vinyl siding) as a sturdy bottom.

I use plastic canvas as well.

I use heavy iron on interfacing..I find it works best for me..

When I get pictures framed I ask for the piece they cut out - I've paid for it anyway - and use those as bag bottoms. Also I've used the premade bottoms I found at a quilt show. I have seen plexiglass ones, but haven't used them. I'll bet the home store could cut them for you.

I'm cheap and I recycle . Buy my salad greens in a plastic bin like container. Cutting out the bottom is quite usable for some purse bottoms naturally covered by fabric but it is clear then easily removed for washing--great for big tote bags. For more fancy purses "Decor Bond" is one product I've used as it is stiff. Variety of ideas fo you