I hit the pacas here (second hand market, all the extra stuff from Goodwill, Salvation Army, etc. is packed up in massive blocks and sold to entrepreneurial spirits here) once every couple of months and stock up on stuff for pennies a piece.
I also tend to buy clothes that are large enough to be turned into something else . . . . my boys have several cute pants and shorts made out of maternity denim dresses and super size tee shirts! I really enjoy sewing so throwing together some very simple play pants is a great solution for us and the boys like it because I can use fun fabrics and patches, or make them matching outfits.