Family dollar has some API SL/SM 10w40, I think the brand is "American", for $1.09. If they have 5w30 it's a dime more expensive IIRC and by then you could buy supertech. They also have some non-detergent 40 weight for around/under a dollar, but that wasn't your question.
Boaz, if your dollar tree still has trop artic, buy a case or two-- the ones around here have been out of stock since August 05.