For many years, I have used paper egg cartons. When you are ready to transplant, just cut off that small section and put it directly in. The paper is compost and will "disappear"

Oatmeal containers are my go to. I save up all summer, fall and winter and use them come spring. The roots don't seem to have a problem breaking through the thin cardboard.

Since my original post I've expanded my use of cheap, free, and recycled pots. I have learned how to make newspaper pots(I love these), discover the value of old toilet paper and towel rolls, and found out that our local recycling center puts all the pots aside in their own bin for us crazy upcyclers and recyclers. Despite using a ton of pots for my starting little market farm, I don't see myself ever buying another pot. Though I still can't live without good 1020 trays. I am still trying to replace those.

In the modern world, going green is complicated. My plastic pots are, well, plastic but they are recycled and reused many times. My newspaper pots have ink in them, but it is mostly soy based and I am recycling once again plus they are biodegradable. At least I see no downside to the towel and toilet paper rolls since most cardboard glues are starch.

Happy growing and loving the earth!