I've checked the official Manchester tourism website and found that most accommodation at less than �100 per night is already fully booked on 7th Ocober:
http://www.visitmanchester.com/
You might like to consider stayingat the Novotel. Not the one in the city centre (which is �149 per night) but the one at Worsley (which isn't that far from Old Trafford). A room there (for a maximum of 2 adults and 2 children) is just �59 per night. Breakfast is extra at �11 per person but you could always skip breakfast at the hotel and eat elsewhere:
http://www.novotel.com
Chris