We bought a couple pallets (4 drums each) leftover from a local airshow for a good price.
If you have any shows local to you, see if you can find a friend of a friend, etc. to hook you up.
They repeat the show every few years, so they didn't want to keep it around that long, and the "teams" wanted fresh oil anyway.
Other than that, I don't know that there is any significant difference in the brands. It's just paraffin/mineral oil.