I'd look on TripAdvisor for hotels with a good price and rating. I don't know how you are getting round, but Old Trafford is pretty easy to get to from the city centre. If it was me I'd book for the best rated hotel you can afford in the city centre, but it'd depend on what else you want to do, or if you are driving down (gives you more flexibility about staying outside the centre or increases parking pain.) There is so much to see/do if you haven't spent time in Manchester and have other interests. Food, music, culture, history, shopping - every interest is covered, if you can accept the weather (but you are coming from Glasgow so there won't be much difference really.) Anyway, enjoy your trip and hopefully it's a good game!