A place that iv been going to with my friends every summer is Allouette Lake in Maple Ridge. Basically if you have any kind of boat (motor or rowboat) you can park your car at the public parking by the beach and buy a bunch of day passes for however long you want to stay there for, and ride across the lake to any of the available beaches. Lots of times the beaches are already taken, but depending on the weather and how far down you go there should be a spot to camp. Best part is its free.