Swans gear can be hard to find in Melbourne, but I found a little shop (factory outlet) at 885 Wellington Road, Rowville (near the corner of Stud Road) that is a factory outlet for AFL, Rugby, Bands, TV Shows etc merchandise.
They had Swans guernseys for $50 and a varied range of other Swans stuff. Changes all the time, but worth a visit if you're in the area.
Most tshirts are $15 - Game Of Thrones, Vikings, Walking Dead, various bands

Open
Wed 9:30 - 4:30
Thurs 9:30 - 4:30
Fri 9:30 - 4:30
Sat 9:30 - 3:30