Feel free to try to Manchester YHA in the Castlefield area of the city centre. The missus works there, and says it"s £24.50 per night in a 4-bed dorm on weekends. Not very glamorous, I know, but if there"s a few of you coming down, it"s easy enough to book out a room if you ring up (but do be quick, as they"re always sold out on Saturdays).
The G Casino is a short taxi ride away, but don"t get it muddled with the Salford Grosvenor which is just around the corner