You might also try Extended Horizons in Lahaina. fwiw Pacific Dive doesn't have their own boat, Lahaina Divers does if that matters. Although I've dove with both and can't say anything bad about either of them, Lahaina sometimes has more crowded boats but generally only on the weekends. We dove with them mid-week and there were maybe 10-12 divers, 3 crew and they have big, wide boats, it was very enjoyable.
As you've figured out, Ed Robinsons, B&B, Maui Dreams and Mike Severns all depart out of Kihei which is a good 45min. drive south of where you're staying. A cab would be prohibitively expensive.
No one on Maui picks up that I'm aware of, unlike on Oahu. I think it's because Oahu has a greater concentration of tourists in Waikiki, Maui's not like that, it's more spread out. Just about everybody rents a car at the airport and drives out to/around West Maui.
There's now a local municipal bus running on a limited schedule since last summer.
http://www.co.maui.hi.us/bus/
But looking at the schedule, it won't be of much use for diving since the diveboats all leave between 6-7am to take advantage of the calmer water in the mornings before the tradewinds pick up. But it might get you back to Kaanapali from Lahaina in the afternoon.
There's also a local shuttle bus I used once when my family had the car, it picked me up on-call in Kihei and took me about 10 mi. north, fare was very reasonable(for Maui) like $5.00. I don't know if they run in the Kaanapali area though. I found it in one of those local information brochure kiosks that are in most of the resorts lobbies.
Most of the snorkeling is done at Molokini, there's the Pride of Maui, it's a big powered catamaran that gets out there in a hurry. They also have tanks and do a resort course type dive for non-certified divers. They do a pretty good barbeque also. But it's kind of pricey.
I think they leave out of Maalea harbor which is 20 min south of Lahaina. There's also a big sail-driven cat in Lahaina that does snorkel runs out to Molokini, I can't remember the name. They advertise everywhere so it should be easy to find.
I'd finish your cert. and go on a regular diveboat though, it's so much better. Chances are good that you'll wind up doing some of your o/w dives at Molokini anyway. If not, Lahaina Divers used to run out there on Wednesdays, it's farther than from Kihei, so they don't regularly go there, instead they go across to Lanai and dive the Cathedrals - another must do dive on Maui.
hth,
