Look for used nursery pots. A 15 gal. pot will probably give you a good yield. Any larger than that, you're looking at not being to move it around at all.

Use 1 x 1's and twine to give adequate support.

Be sure to use potting soil, not dirt or bagged topsoil.

wine barrels can be cheap, depending on how you source them. if you get them straight from wineries and cut them in 1/2 yourself you can save a lot. and don't forget to cut a couple 1" holes and put a screen or landscape cloth on the bottom.

they can be difficult to move, you basically have to roll them on their bottom edge once filled with dirt.

Or put them on a hand truck or platform with casters on the bottom.

I've been using the SAME large heavy-duty rubbermaids to grow tomatoes for the past ten years. The boxes sit inside the lids which serve to keep the greenhouse cleaner and reduces the amount of watering I have to do. (You will need to drill drainage holes in the bottoms of the boxes of course!) I use garden soil amended with lots of compost and manure and add organic slow release plant food plus dolomite lime when planting. The soil gets changed every three years. To support the tomatoes, I buy a bale of sturdy 4' wire and make cages that stand inside the boxes. The wire has to have holes large enough to put your hand through to allow for easy picking and pruning. I can then stand the boxes in rows and use a drip irrigation system to water as required. Rubbermaids often go on sale. They resist ultraviolet light quite well. The lids are now starting to break apart, but the boxes are still going strong. (The wire also makes great cages for other plants that need support or be protected from deer.)