I've been diving since the summer of 1995. I've dabbled in many other sports since then, but diving has never fallen below #2 for me. For those willing to commit the effort, and who can tolerate the California waters, it is a highly rewarding pursuit.
Required equipment - considerable. To dive in Monterey, you need a drysuit or a well fitting 6.5+mm suit. You need a hood and booties, and most will need gloves as well. If the water is above 53, I will often forgo them so I have better dexterity for the camera, and the ability to feel texture. Next, you need a tank, a BC to hold it, and a regulator with two second stages, and a pressure guage. A dive computer is a good idea but not absolutely necessary. Then you need a mask and fins, and a good dive light. Last, a weight belt with 15-30lbs of lead.
You can rent most of this, but will need to buy the basic snorkel equipment (mask, fins, bootie, snorkel, gloves) which will run you 200-300. You can get a decent small light for 30-40, a good cannon for 80 up. A simple pair of shears is 15-30. Not all rental rigs include a compass or a dive timer, so you probably want to consider getting those. The remainder can be rented for ~50/day, or 70-80/weekend. To buy this equipment instead will probably cost upwards of $1000, but depending on your choices and shopping ability can be done between 500 and 3000. Look to my main diving page for individual purchase suggestions.
Required time commitment- 2 full weekends to 5 weeks of part time work for the certification. Diving itself is a full day, a weekend, or perhaps a week in some tropical paradise.
Costs - divers need to have a C card to rent or buy gear, or to dive on boats and get air fills. This isn't totally true as the system is voluntary but you will be seriously limited without the card. And you'll probably be at risk. Diving is one of the more dangerous recreational sports in terms of fatalities. When sometime goes wrong underwater, death is a distinctly possible outcome. Get the training - the OW cert will generally cost 600-700 in the Bay Area (including the required snorkel gear purchase) when all the costs are added. Classes are advertized from $99 to $300, but most of the differences are in which fees are added on later.
We are fortunate here in that Monterey shore diving is nearly comparable to boat diving, making boat charters a luxury expense. Even if you must rent all the gear, it is about the same costs as skiing when you do own your gear. A single air fill is about $4 and can last 30-80 minutes, depending on depth and experience. Figure on doing up to 3 dives in a day.
Where to dive:
Monterey is the closest game in town to the south. There is almost no diving between Marin and there because of poor visibility (primary reason) and perhaps too many sharks locally. The area between Half Moon Bay, the Farallon Islands, and Pt Reyes is called the Red Triangle and is one of the 3 hot spots in the world for white sharks. This shouldn't alarm you too much - surfers are far more likely to be targets and still the state has 1 or 2 attacks per year, total. Fatalities are close to one per decade. The drive down to Monterey is far more of a risk, especially on the way back when you're tired. I've even been out to the Farallones twice and didn't see them there either.
Monterey and Carmel offer a lot of kelp diving with more color than common to Hawaii and other tropical spots, and much better reef life diversity than seen in the Channel Islands. Fish life is much less so, however, though marine mammals are plentiful and will be frequently encountered.
Well to the north, there is also diving on the Sonoma and Mendocino coasts. Most people there free dive (no tanks) for abalone, but I've enjoyed the tank dives I've done. Often though, it is a bit of a hike from the car to the water.
My main diving page .
My UW photography page .