https://www.google.com/travel/hotels...oCCAQYAJIBAiAB
^^ this place is $109 a night right now. never been there, make no recommendations but it appears to be in the heart of Annapolis downtown. Do a google street view and walk down the streets to see.
Like everyone has said, the DC metro is very expensive. The area anywhere around Landover has 0 to offer but will run you probably $150 plus for a crappy motel 6. Hotel in DC or Northern VA would probably be 300 plus.
I would suggest staying in Annapolis. its beautiful, lots of restaurants and is great for walking and seeing stuff. Its probably 45 miles from the stadium but if you rent a car you can drive in and park. Or drive to the nearest metro station and take the train in. The drive is easy. Straight shot down Route 50 to 495 then follow the traffic to the stadium.
*** definitely eat at Chick and Ruths Delly (old school diner) and get the crab cakes. You only need one, not two .. the best ive had.
*** if there is a Navy home game or any Naval academy thing going on that weekend, Id imagine they would be booked. The Naval academy is right there.