I actually stayed at Motel One earlier this month for a night. Pretty nice for the price and convenient -- good choice. It is right next to the train station, and the ride to Etihad is only about 10-15 minutes. However, the crowding on the train both to and from the match there is just about the worst I've seen in England based on the two times I've been there and makes the standard NYC subway commute look spacious. However, you can actually walk to the stadium in about 30+ minutes and there is a pretty easy path with good signage and lighting. Just a thought for those of you who, like me, like to walk and prefer not to get jammed into a subway car.
Have fun -- should be a very cool trip.