It really does depend. About ten years ago we went to see the Raiders in Oakland and they were virtually giving the tickets away. I can't remember exactly how much I paid but five adult tickets were less than $100. (That's $100 for all five, not $100 each).
And for those who don't like the game...
I was thinking that, surely it sells out well beforehand?
Mind you, I doubt many paying those prices will leave 10 minutes before the end to beat the traffic!