also where can i get some cheap?

A small % of castor will give some added protection at higher temperatures, (it has a higher "flash point" than most synthetic oils) and will also help protect the steel parts from rusting, because it leaves an oily film on the parts.

Try a motorcycle shop...or anyplace that has supplies for 2 stroke engines. You can add 3-4 oz. to a gallon for a little extra protection.

In an R/C car engine, too much castor can cause the one way bearing to get sticky after a while...that's one reason why you don't see castor advertised much in r/c car fuels. (they're mostly a high % of synthetic, or all synthetic)