6 inch square pot alternatives??

So I'm looking for some cheap 6 inch square pots alternatives. My local hydro is charging an astronomical amount for the purpose built ones. 5 quid a go. And I need 20 of them. No chance I'm paying that much. Currently I've only thought of childrens sand buckets which are relatively cheap. Around 2 quid. But can you think of any others???

Actually can you think of any alternatives for anything that we growers may be paying top dollar for???

i get all my pots at a local feed store/greenhouse. i get the basic black plastic platers, used, for very cheap. like 1$ us for pretty much any size. look for a local nursery and check into used pots

Unfortunately my friend I live in a country where everything has astronomical prices. And my Credit cards maxed out.

Use the plastic 4L empty milk jugs, there square and they must be 8" - 10" just make sure you clean them really good and cut off the tops

Cup work ok, but are top heavy and get 4x waters a day.

oooh. 4 waters a day!!! Thats quite a bit. Today I've actually came across a pack of 8 x 2litre bottles of water for 3.19!!!!
Even better they're deeper than the square pots so more room for roots.
Thanks.