Eurocon attendees have a choice of loads of hotels and B&Bs in Manchester, including some which are a short walk from the Eurocon venue:
Ibis Hotel - very close to the Lass O'Gowrie
Premier Inn - a few minutes' walk away
Unfortunately the nearby Days Hotel is already fully booked for 3rd-4th September.
Both the Ibis Hotel and Premier Inn currently have special offers where you can get a cheaper room if you pay the full amount in advance (check their websites for details). Otherwise you will need to provide a credit card number to reserve a room.
Please note: if you decide to book a hotel room with no breakfast, you will be able to buy breakfast at the Lass O'Gowrie on the Saturday and Sunday.