For smaller stuff you could use glass jars for salsa, jelly, etc. any tin containers you might have. For bigger stuff you could use pallets that haven’t been treated with methyl-bromide to build raised beds or use it as a plant stand. Or if you want to go the rural white trash route you could use old tires that you paint usually some pastel color.

I’ve seen a neighbor use milk crates lined with old t shirts, but if you’re putting the planter directly on the dirt you only need to line the sides with newspaper.

A lot of people use landscape fabric to line them, which is overkill and prevents the bottom of the soil from coming into contact with the ground. You want the worms and good bacteria to go up into the planters.

I use yogurt containers

If there are plant nurseries around, you might call them and ask if they have anything they are going to throw out. There’s a chance they get things shipped and then repot them. The worst answer you should get is a “nope”.

Got any hippy food stores around that have a bulk section? or any place with large scale kitchen? Call and ask if they’ve got any buckets, liquid containers that they’re just going to throw away. I’ve worked in a grocery store with a bulk foods department, we’d be willing to give away empty 2.5 gallon, 4.25 gallon, 5 gallon buckets, the large paper bags that held beans/rice, the 5 gallon jugs for Tamari/Shoyu/Honey/Vegetable oil.

Kitchens should get a lot of food service sized containers of olives, mayo, vegetable oil, tamari/shoyu. All of these can be cut up and used for planters for at least 1 season (assuming you aren’t worried about using plastic.) You might even get lucky and find that they have gallon or larger sized glass jars that you could use as planters (probably wrap them in a few layers of paper to keep the UV from nuking the soil if in the sun).