I concur, I just picked up a bottle of 3 in 1 at walmart a few days ago for 2 bucks.For storage, a heavier oil such as the 3n1 household oil would work fine.
I just use the spray can that I bought for my bicycle called Tri-Flow, great stuff. Any oil will work though food grade oils can spoil and are not recommended.
You should be able to nab some AK47 bayonets that are sealed in plastic, coated in cosmoline, for pretty cheap.I need to plant a few fixed blades outside to grab at a moments notice. These would be out of the rain but subject to high humidity. Is there an oil I should use to preserve the metal? thx