In case some of you might like to try making your own, here are the instructions I came up with after a couple of tries:
Here's what a plain finished bag (about 13 x 15") looks like:
And here's one with a tie (I used some nylon ribbon I had on hand):
The fabric I had on hand was 120" wide, so on only a few of the bags I made could I take advantage of the finished selvedge edge. I will look for 45" material to make more bags. Here are cutting instructions for 45" fabric (see end of post for note on using 60" fabric):
And here's a sketch of the sewing instructions:
Here's a bag cut, pinned and ready to be sewn. On this one, the selvedge is at the top:
You do need to make French seams when sewing the edges, as the polyester frays badly in the wash. But it's very simple. Sew all around the right and bottom edges, where the pins are in the photo above, using a 1/4" seam. (The fold is on the left and the opening at the top.) Then turn inside out, and sew the seam again, using a somewhat larger seam so that the first one is encased.
The last photo is a close-up of the top edge (here, selvedge), and the French seam, which sticks up a bit.
No more plastic bags, yay!!
About cost: 60" fabric would yield 3 bags from 3/4 yd, about $1 per bag. It looks like 60" may be the narrowest I can get in any case when I go to buy more. So--the cutting instructions will need to be modified above, so that a third bag will come out of the "waste section." This middle bag will have no selvedge edge, so the top will need to be hemmed.