I wonder if it is maybe a bit more difficult to get a guy to buy into a woman's expensive sports-related addiction than vice versa, though this may have just been my personal experience!! I guess I always thought that women expect this of most men, but it is not so easy to convince a guy that you should be able to take a $5000 trip (especially when he can't always accompany you)...
I did not try to rationalize. I was honest about loving this stuff, and that worked for about 5 minutes, and then - not so well. So, I tried to get him involved. I also tried to reason with him that it was my passion. Finally, I tried reminding him that I was spending my money and not his.
After a couple of years, I gave up, became single, and dove on my own - and eventually wound up replacing the guy with an underwater photographer of nearly 30 years who loves that I talk about lenses during our morning runs, that I converted our 3rd bedroom to a camera room, and that we have a large part of our household budget set up for EANx fills, weekend charters, and trips.
(Not that I recommend taking this route, of course...)