Parking around the gym is free.
On the gym road itself and on surrounding roads.
There are 3 close car parks on:
Higher Barlow Row
Canal Street
Mottram Street
During class times the surrounding businesses are closed and there is ample parking on the street itself
During business hours Mon-Fri 9am-5pm the street can be busy with businesses being open, my suggestion is to find parking on one of the streets mentioned above and walk over.
Stockport