How cheap?
If no luck second hand, you can get big cheap pots from asian grocers.
Not necessarily amazing quality (I had a ball valve literally pull away from a wall but after multiple, frequent and regular use) but ok if not tampering/drilling.
Otherwisr chefinox aluminium pots from hospitality suppliers. Cedar in brunswick do good prices (years since I went so caveat) and may do online/delivery too.
80ish for my 40L alu pot, 4mm but that was at least 5-6 years ago.