I was a MAC user and recently changed to Diorskin Nude Foundation which is only 47.00 and it's great. I love it. It's a mineral liquid foundation which keeps the skin hydrated also has SPF of 10 (any bits help right?) and it's a matte foundation. It's nice and smooth, gives a natural finish and feels like I've got nothing on at all and it doesn't cake. I think it's recently priced for how many benefits this foundation includes. Good luck!
I like Clinique Superfit foundation. It has some fancy sweat-wicking technology, something like that, that keeps your face dry. It gives the face a natural matte finish and I really like it. It goes on smoothly and not cakey. Hope this is a good match for your skin
You may want to give Clinique's Stay True Makeup Oil Free Formula a try. It's a favorite with oily skin types, it minimizes shine and leaves a matte finish without clogging pores. You can find it at: http://sephora.com/browse/product.jhtml;jsessionid
I hope this helps you.
Next time you're at the drugstore check out the cover girl clean collection. There's a foundation for almost every skin type and it's affordable.
Also check out the healthy skin foundations from Neutrogena. I don't know if they're oil free but you can go to their website and check.
Other ones that I like (but alas are not as inexpensive):
Make UP Forver Mat Velvet touch makeup (have been using it more lately and it really is excellent) http://www.sephora.com/browse/product.jhtml?id=P17
MAC Pro longwear foundation
Estee Lauder's Double Matte foundation
Clinique's Superfit foundation. http://www.sephora.com/browse/product.jhtml?id=P22
Hope that helps!!