I want to buy seattle mariners tickets for the september 28th game?

I have a family of 5 my youngest is turning 12 and I would like this to be one of his birthday gifts, my wife and I and our 3 boys (17,16,11) I would like to know how much it would be for all five of us to attend.mariners will be playing agaist the oakland Athletics the night of the 28th of september , we will be traveling from spokane area to attend game, I looked online and tried the online ticket sales with no luck