A bit out your area, but its free:
Try the Function room in the Powerleague Soccerdome near the Stadium, big enough for 80 and is a free room as long as a certain amount is taken behind the bar (about £250 IIRC), though you need to pay a deposit (about £100)which is returned once the money behind the bar has been calculated.
We had a party there in March and it was an ideal venue with decent sized bar and dancefloor.
If you've ever been in the soccerdome its on the upstairs level on the right hand side opposite the kids play area. Wigan RL use is on occasions - Max the Warrior events, Cheerleader training....etc!
01942 210080