that walmart 2stroke oil (forget the name) is just fine if you mix it at the correct ratio 28-1 ( or 25-1 can't remember), lots of people run it. It smells crappy but it will get you through a pinch.
I actually ran castrol outboard oil, $9 for a gallon, it built up alot of spooge and was a bit rich but it got me through the last of the riding season last year, even broke in a top end with it and its still in great shape.