So imagine my delight when I discovered the Cambridge Community Scrapstore. This is a place you can go that's just basically a big warehouse full of crafting bits and bobs. I bought a membership and have been a few times, filling my cheek pouches with bits of fabric, card, and miscellaneous junk.
Among the things I got on my first trip were some sheets of fake grass material. I marked out some rough shapes on the back of the sheets with a silver Sharpie, then cut them out with a utility knife.
At this stage, I also brushed the fake grass material a lot because it sheds like mad, especially if the cuts go through the base of a tuft.
The base of the material is flexible, but I wanted to stiffen it a little, so I hot-glued the pieces to sheets of card, which I also got at the scrapstore.
I then cut out the shapes, leaving a little bit of a lip around each one. After cutting out about a third of my grass material, I had enough to fill a shoebox.
These pieces then got a bead of hot glue to seal the edge between the grass material and the card, then a layer of PVA and sand. I let that dry, then painted it light brown with a lighter drybrush and called it good.
As you can see, they're a bit rough and ready, but at a price of pennies I'm perfectly happy with them. They'll serve as reed beds in Frostgrave: Ghost Archipelago or my Crusades games, or long grass in other settings. Here's the same patch of long grass with a model for scale.
Apparently, these scrapstores aren't uncommon, so if you like to trash bash you should see if there's one in your area. I expect more frugal gaming posts inspired by the things I find there.