Most dealerships/warranties consider up to 1qt every 1000 miles acceptable. Sounds like you shouldn't be buying used cars. I would suggest you look into a lease instead... the cost of ownership is fixed and predictable. At the end of the lease you just give it back.
As a sidebar I've been buying at wholesale auctions as a consumer for many years now. Most of these auction services offer post sale inspections which include provisions to terminate a bid if vehicle is found to contain defects not disclosed. Also most of the vehicles I buy are usually off-lease and being sold by the leasing company or bank, not a dealership and not lot left overs.