If I may join the OP in asking, what oilless/waterless compressors have a good track record? They are on Amazon and Ebay in the $200-$400 range. And they are limited by design (because of overheating) to direct filling the airgun only, or 0.6L or less capacity bottles.
EDIT: what happened to the Altaros mini compressor? Haven't heard about it lately. That one I think runs full-time and does not need oil or water.