beer keg. fits 15lb (15gal) perfectly.
$25-50 off craigslist in almost any town.
you can cut the top off, or get fancy and have a 4"/6"/8" tri-clamp ferrule welded in instead of the sanke tap.
you might find one already altered (keggle).
https://www.google.com/search?q=keggle+or+keg+site:craigslist.org
add your local craigslist into that query to see only local hits.
eg keggle or keg site:portland.craigslist.org - Google Search
you can extract in them unaltered.
but should probably read up on how to empty them if you want to go that route.