Upvote:3
The easiest cheap way is BC Ferries, from Tsawwassen or Horseshoe Bay.
Steps:
(source: I've been to both Vancouver terminals, and taken the ferry to Nanaimo and back twice, both times from Horseshoe Bay).
There are flights (check kayak.com) but the ferry will be considerably cheaper.
Upvote:4
You can fly in 20 minutes, tickets from $75, or take a ferry in two hours for $11-13. Bus #5 goes to the ferry terminal at Horseshoe Bay.
For this and any other "A to B" question: http://www.rome2rio.com/s/Vancouver/Nanaimo