Um, well there's an old drag trick where before you put on your foundation you brush on a layer of milk of magnesia on before putting on your foundation. It's pretty common and some people swear by it: here it is on makeup alley I don't 100% condone it though because it is not meant for the skin, I suggest doing some research on it if you're interested. Some other products that might work for you is make up setting spray or primer.
A good cheap foundation for oily skin is Revlon Colourstay for oily/combination skin, it is kind of runny though. Besides that I was thinking of some other foundations but I think they are also in the MAC price range, they are really thick though basically the consistency of concealer, because of that, they will also last you a really long time:
Kat Von D Foundation
Kryolan Foundation (or paint stick)
RMCA foundation (you can buy a sample online here for 4 dollars) and even that'll probably last you a while.
Also I don't mean to pry, but I'm wondering are you doing any skin care regimen or cleansing before you put on your make up? I'm just wondering how it can be soupy from the very beginning.