When I signed up for diving it was my first really expensive hobby. The instructor said to just buy the fins, mask, suit, and belt. Instead of an octopus get a diving computer and never buy tanks unless you live close to where you dive. I agree with you up to a point but there are logistical problems with your argument. Some of the best diving places are only available by flight. I'd rather spend the money diving than on shipping tanks across the country.

Also, a good dive shop has fairly new equipment for rent. If they are good at what they do then it will show in the quality of the equipment and staff.

Now that I have kids I still consider it a hobby. But one I only get to do once a year. I've added a few more expensive hobbies to my list since exiting my broke college student phase: International travel, photography, and wine.

BTW, every good salesman I've met has expensive hobbies and a rich spouse :-)