The only oil I have heard of cheap was imported was from Nigeria. I did ask if he supplied snake oil as well, and he said he was able to get snake oil at a reasonable price. (not often you meet someone advertising they are a snake oil salesman) Funny the next spammer on the forum said they sold snake oil as well...
I think the magic ingredient is likely to be a solvent to make the oil thinner. Unleaded probably does as good a job per litre, and would do a better job per dollar. I think its already been discussed on the forum somewhere.
Dont be afraid to get plently of knockbacks when asking for oil. I found riding on the pushbike a good way to find the backs of the shop, and if there was a 44 gallon drum out the back. I asked at the places I couldnt find a back of the shop, and had success.
Best of luck with it.