Old Goat, I have been known to use "recycled" items for molds, including the following:
- Various plastic storage containers, even including Cool Whip containers
- Cheap 1 gallon plastic pitcher (< $3), with the bottom and top area (where the spout is) cut off
- A drywall compound bucket, well cleaned and run through the dishwasher repeatedly - hey, it's exactly the right kind of plastic, and it is heavier-walled than many plastic storage containers, and it even has a nice little cross-hatch pattern on it.
For any of these, I have drilled holes as needed for drainage.
All of these have one characteristic in common - they all have just a little bit of "draft," or slope to the sides. In practice, as long as it is just a gentle draft, I have not found this to be a problem, and may even have some advantages. As the cheese is pressed or drained, you typically turn it periodically in the mold; with the slight draft to the molds, it helps to compact the cheese a bit more each time it is turned.
The one thing you have to give some thought to using a mold with a bit of draft is the size of follower that will be needed (if the type of cheese made with the mold will be pressed). You need something that will not wedge itself short of the final height of the of the cheese, but at the same time will not be so small that you get a lot of cheese pressed up in a ridge around a too-small follower. Using cheesecloth that is carefully pulled tight will help reduce this problem ... and a little bit of a ridge just means you have something to trim it off after removing from the press, to enjoy an early taste of the cheese.
I have cut followers out from inexpensive plastic cutting boards - I bought a 1/2" thick plastic cutting board on Amazon and rough-cut it into the sizes of followers needed on my woodworking bandsaw, then sanded it down as needed using a drum sander with a fairly low (rough) grit - don't use a fine grit, or it will just melt rather than grind/sand. You can do final smooth with finer sandpaper by hand.
I know that several folks have used PVC pipe to make molds, and these have the advantage of being (1) very sturdy and (2) straight sided. I have always been a bit hesitant to go this route, since I've read that there can be some issues with chemicals leaching from the PVC. But others seem not to have any issues with off-flavors, and I confess that I have been quite tempted to give it a try ...