Keep your eyes open when you're out and about especially driving around in neighborhoods. I get most of my pots for free because people will put them out on the curb. Always ask first tho:). It's getting warm now so people will clean up their yards. Put there old pots out and their junk is now your treasure:).

You can reuse your plastic pots too. They always don't need to be put in a different pot. Sometimes when I get a new plant, and the plant still fits perfect in the pot it came in. I will just get all the old mix off the roots and change the mix out to my mix:).

Do you buy your plants at a nursery? If so, you might ask them for any cast-off pots they would be willing to give you.

If you notice someone in your neighborhood gardening, ask if they have any extra pots they would be willing to part with. Most gardeners have them. You could offer to help him/her with a chore in exchange.

Some nurseries will also have a recycle bin for cast off plastic pots.

Also pls try posting & or looking for them on your local 'Freecycle'. I've sometimes seen such listed here in NYC (for both plants & gardening supplies on occasion).

urbanore.com/

Urban Ore in Berkeley has plastic pots, lots of 4" and other sizes, they also ussualy have some terra cotta and other ceramic, metal etc. Super cheap, like .50 each for decent used small terra pots. Plastic 4" are like 10 for a dollar or similar. In Berkeley near Ashby Ave and the freeway 80. I also get a couple of cheap terra pots every time I'm at the goodwill store, usually a couple buck each or nice glazed ceramic one for around 3 bucks. I've collected hundreds this way over the years. You can also buy cheap NEW plastic pots at Orchard Supply Hardware if you want clean and new. Lastly recycle centers, like where you take your cardboard, plastics etc. in your town.... mine and many others have a book exchange and garden supply exchange, lots of free plastic and terra cotta pots, 1/2 bags of soil, old hoses etc. Call around, theres one nera my house and I stop there when I have an extra minute, pays off over time:-)

You can go on Mercari (website or app) and get them really cheap. You can get $2 credit if you use the code FTBBYE.

You can really use any plastic container just drill some holes in the bottom.

Yogurt containers, plastic drinks cups (like a red solo cups that are everywhere after that annoying party in the apartment upstairs, for example), cut off soda bottles, etc. cut down milk cartons,

Plant containers are everywhere.

Also, thrift stores may have pots. Just be sure there are drainage holes

Definitely thrift stores. They often have handmade ceramic that can have some interesting looks.