Of the two, plane vs. helicopter, flying in a helicopter for the first time is without a doubt more exciting, but costs about 3x as much.
The Dean River logistically tough to do without doing a trip to one of the 4 lodges on the river, and no matter how you do it, it will be expensive. You have 3 ways in, once you make it to Bella Coola;
1) West Coast Helicopters flies a A-star, that they charter out for a couple grand per hour, so most people either get dropped on a stretch or river where they can camp or do a float trip. An A-star has about as much room compact SUV for gear and people, so in order to do a float trip, it will probably take two trips with a helicopter, one for people, one with a net load of gear. Helicopters don't ever fly with a net load and passengers at the same time, so you're looking at two round trips. If weather is good, the pilot can fly in a straight line between Bella Coola and the Dean. If weather is poor, he'll have to follow the coast line and fly up the river. Its longer and thus more expensive. Most people try to fly in as another party flies out so they only pay one way.
2) Bella Coola Air flies in to the air strip with Cessna 172 wheel plane or to the beach with a 185 floatplane. The flight is significantly cheaper than the helicopter, but you're limited to fishing the several kilometres below the canyon because it would take most of a day to hike your gear above the canyon and then you'd still be pretty limited in terms of water you could fish because the shores are thick with cottonwood saplings and often cut banks. If you fly into the lower river and tent, you're still limited in terms of water because hiking along the lower Dean is also difficult and its somewhat busy with guided clients from BC West, Blackwells, Cedar Hole fishing club.
3) Not fly in, but you can also hire a commercial fishing vessel out of Bella Coola to take you and all the gear you want to the beach near the airstrip. The fishing vessel can tow a jet boat if you want, which would give you better access to the lower Dean.
There are enough wealthy people in the world that the Dean, while not crowded, is far from remote feeling. I'm not sure you'd feel you'd get your money's worth on a do-it-yourself trip to the Dean unless you planned way in advance and were experienced wilderness tripping. Not a first-time trip. I'd feel you'd get more for your buck if you could stay at one of the 4 lodges; Blackwell's, BC West, Lower Dean or Hodsons. The challenge there is that prime times are booked well in advance and return customers get offered prime weeks and it'll cost around a grand/day for around and you'd be there about a week.
Locally, Valley Fishing Guides out of Squamish does helifishing to the upper Pitt and several other coastal systems.