I was checking amazon and home depot, and 12” sturdy plastic saucers begin at $3.50 each. I find them expensive.
Is there any way to build these saucers for cheaper? I searched pinterest and there aren’t many diy for saucers.
I'm pretty sure its not possible to make your own plastic 12 inch trays, but you may be able to find another way round it. I don't know whether you mean for use outdoors or indoors, nor whether you really need 12 inch trays rather than something a little smaller, but I save some recyclable plastic trays originally acquired as part of packaging on vegetables, and saucer-like containers which previously held microwavable foodstuffs for use outdoors, especially the larger ones, but none would measure 12 inches, more like 8/9 inches. And like most gardeners, other items are repurposed rather than being thrown out and are pressed into service outdoors - a couple of old, round, plastic trays 11 inches across (good for larger pots) as well as 2 or 3 ex tea and dinner plates that are no longer useful indoors. Old crockery would certainly be of the size you're looking for...but that's only helpful if you've got stuff you can repurpose.
Indoors, I prefer to use proper cache pots, but many of the ones I have came from charity shops (known as thrift stores in USA). Gardeners generally tend to be imaginative, thrifty people when it comes to this sort of thing, preferring to repurpose objects where possible rather than throw them away or buy brand new. You may be able to find crockery dinner plates in a thrift/charity or secondhand store of the right size more cheaply.
I would just add though, that price you've quoted for 12 inch plastic trays is really cheap - it equates to £2.73 in pounds sterling, and I recently paid £3.00 for a 6 inch plastic tray for pots in a local hardware store.
Making the kind of plastic saucers sold at stores is nearly impossible unless you have access to plastic molding equipment.
But I recommend you think outside the box and remember that they are called “saucers” for a reason - our grandmas probably used real saucers or plates, either very decorative ones matching decorated pots (think Victorian estates) or simply chipped ones that got a second life after serving as regular tableware. The purpose of a saucer is to catch excess water, protect the surface underneath and for some plants, hold a small reservoir of water. Plus it needs to be waterproof and non-corrosive. Any container that can fulfill this purpose can be used as a saucer - so get creative, either check what you already have or what you can find, used or new. I personally own maybe three or four “regular” plastic saucers. The rest are everything from repurposed glass bowls to elegant cache-pots.
I use pie or cake tins, and sometimes small aluminum cookie sheets, purchased at garage sales or thrift shops for maybe 25 cents each. While not plastic, they're certainly durable. Eventually they'll rust inside, at which point I recycle and replace.
Following Bamboo's and Stephie's advice, you could also purchase tons of old plates from these same sources, probably for less than a dollar. The plates could be particularly decorative for outdoor pots (bring them inside for the winter, though).
I cut the bottoms from PET clear plastic bottles , sizes are not very large. I also have a couple ceramic coated aluminum frying pans thrown out by a neighbor, removed the handles. Occasionally you can find a plastic planting pot with no drain holes and cut off the bottom (they likely came with pond plants that love water).
The short answer is NO. You can exactly melt plastic meld plastic in your basement.
You could come up with ways around it by trying something else, like; make hypertufa then seal it. Then you spent just as much.
Terra cotta are often less expensive than plastic.
Try the dollar store.
Pie tins are cheap.
Keep an eye out for used one on a local website.
Post an ad for used ones on a local site.
Buy bulk directly from China. I could go on and on, but there is no way for you to make these safely in your residence.
I use thrift stores. Sometimes I find actual clay plant saucers (.50 cents) but mostly I’ll buy dessert/salad plates to use as saucers.
Contrary to other answers, you can certainly recycle used HDPE plastic into "new" products at home. First you must locate suitable plastic (looking at the recycling numbers on any used plastic you already have). Then you chop it up, either manually or using some kind of shredder. Then melt and form, being careful to only use shop tools, not your kitchen oven.
However, it's unlikely that this will actually be cheaper for you, in terms of buying tools (unless you already have a shop toaster-oven) and also time spent. Even finding enough of the right kinds of used plastics can be difficult sometimes. Better to reuse instead of recycle.