Depends what you are after really, however these are pretty reasonable, dependent upon exactly what they have when you walk in the door.
Camera Lane in Little Bourke Street on the corner of Hardware Lane, gem of a place, plus the owner does know his stuff.
The Camera Exchange in Lonsdale street is interesting in that they literally could have traded 10, 20, or more cameras and their associated gear from somewhere, or have little. That said there is a lot of stuff there, just stuff and more stuff and more stuff.
Michael's on the corner of Elizabeth and Lonsdale streets has a window display. This place is always the top dollar price wise, of all camera shops in Melbourne. Whatever you do in Melbourne, walk into Michael's and walk up to the top floor to their museum, it is one of the finest museums of cameras in Australia, if not the best. It's free too!
Camera Action on the corner of Elizabeth and Little Bourke street, has a few things in their side window. They are mainly an electronic camera store now, which is fair enough as it brings the money in.
As you are down in Mornington way, if you are travelling on the train, get off at Bentleigh. Alongside the railway line is a small shop called Photographic Warehouse, this is a real camera shop for anyone into film. Packed with enlargers and all sorts of weird and funny items plus some very serious cameras of whatever vintage. Not cheap, but if you want it, it's possibly here. I'm not sure of the address, but it is literally a stones throw from the Bentleigh railway station.
Mick.