All is relative I guess.
Some sports are considered sport for rich people, if you then asking people pursuing these sports they 'll say.. no it's not that costly... if you do it this or that way...
I believe in the end it depends on disposable income, value of time, how equipment intensive the hobby is and then the relation to how serious you take that specific sport/hobby.
For diving, if you buy state of the art equipment, do some photography on the side, want everything in titanium... and then only dive 1 week a year on a tropic holiday... I would say yes it's an expensive hobby. If you dive 150 dives locally and on holiday then no... it's not expensive.. he's just serious about his hobby (at least that's what I'm saying my girlfriend
)
I do believe that all pasttimes depending on specific specialized equipment are going to get expensive. The grossmargin on specialised leasure activity goods are incredibly large... and how bigger the toy how bigger the price
Take flying, yachting, car racing.. that's expensive