I would recommend using priceline.com. I use the bidding section. I have been booking my hotels with them for a while now and I have no problems. I got a Residence Inn/Marriot for the Lions game for $50 plus Tax, which was about $65 with tax. That hotel usually runs between $150 and $200 without Taxes. It's a 2 1/2 star hotel. Very nice hotel in my opinion. But this was for Sunday after the game, I am sure that saturday will be a bit more. The only drawback of course is that you can't cancel because you have to pay up front and you can't choose the hotel. Also, You can only choose the general area which I always choose Reliant Park/Medical center area and I am never more than 5-7 miles away.
I usually bid for a two or two and half star. I don't like bidding for three star Hotels because many charge for parking. And it's not cheap.
As for paying for a regular hotel, they usually run on average between $80 and $180 around the stadium. Unless you wanna pay $40 for the dump called motel 6.
Since you are gonna stay for four days, I am sure you can a great deal through priceline since Hotels wanna fill every room possible.