The most common way of getting to Saltspring is to take the ferry from Scharwz Bay on Vancouver Island.
The trip is a very beautiful ride ending up in the bay at Fulford Harbour.
It's a 35 minute ride and the ferry runs 7-8 times a day.
Hitch hiking is totally accepted among all citizens of Saltspring because the busses are very infrequent and quite a few people have no car.
Forget about your usual paranoia and stick out your thumb, just like the little school gorl and old grannies do on saltspring.
You won't be considerd weird at all for doing so.
The ride to and from Salt Spring on the BC Ferries (250-386-3431 or 888-223-3779) is a great way to see the gulf. This is by far the best way to get to and from the island.
If you have less time (and more money) you can use a seaplane. Salt Spring Seair (800-447-3247), Harbour Air (800-665-0212) or Pacific Spirit Air (800-665-2359) all serve Salt Spring. A one-way ticket is about $60 Canadian.
It is best to have a car (or mode of transport on Salt Spring), but you can hitch a ride from the ferry into Ganges quite easily.
Please note that there is NO public transportation on the island. You will have to either drive, or rely on taxis (which is not really feesible and will get expensive)