you would be looking at around 150$ for for food grade 44-50Gal just under 200L drums, in my exp.
if it smells okay it should be fine for mashing in, i am sure you can see what i am trying to get at here.
if you can get a hold of one clean it down with phosphoric or something then see how it holds water, i.e give it a taste. worst case you've got a nice rat proof grain bin.