I generally do 12 gallon batches.
Found an aluminum 80qt (heavy duty) on Instawares for less than $100.
Mash in a 70qt Coleman Extreme
Natural gas fired on ring-burners
Heavy-duty 1/2" Cu immersion chiller with an ice-water recirc.
Currently wort is transferred with a gallon pitcher and filtered through a China-cap or sieve. Modifications underway to install kettle-valve for my March-pump to transfer instead.
Ferment in 7.9 gallon buckets inside 40 gallon plastic totes chilled with frozen soda-bottles.
It's easy to step down to 6 gallon batches since it's hard to drink 12 gallons of an experimental brew gone awry...
Here's my ghetto setup: