http://www.sgccard.com/MonthlySpecials.aspx
They did have a $6 grading special at one time last year. But it may have only been for standard sized cards, because they would not let me send in a set of tobacco silks (just a little larger than T206s) since they would use a non-standard gasket.
The current $7 one is only for 2000 and newer cards. Seems weird since they are not known at all for grading modern cards...
I would reload the page each month until you see the one you want.