This is about half the price of the normal entry charges, so is a decent move. The board did it twice last season when we played Dunfermline and Inverness Caley Thistle, with the former seeing a record attendance for the ground - although it was quite an important game!
It should be pointed out that this match does have some meaning - Saints avoiding defeat will officially send Gretna down.
Story source: The Official St. Mirren Website