I have used new car engine oil for years, never ever had a problem & never had any dirt/dust get past the outer filter element. At the moment I'm using 20w/50 Castrol GTX & it only cost $5 for 1 litre here in Australia, probably cheaper in the U.S.
It last for ages, costs bugger all & does a great job, & I can wash them out easily in hot water & dish washing liquid detergent.