Cave diving equipment is expensive! Where can I get it cheap?
There is no good answer to that. The problem is, what equipment are you going to use? Brand A may be widely available, and widely discounted; Brand B may be manufactured in small lots, available only directly from the manufacturer, and require a mortage on your house! Until you take your course, learn about and decide on which equipment you will need, you really shouldn’t be spending a lot of money up front. The exception to that guideline is, if you have a dive buddy who is a cave diver and he/she wants you to dive with the same gear and configuration as them, then your problem is easier (but it’s still a problem). This isn’t necessarily the best approach, but there is some validity in having the same “kit” as your primary dive buddy. But if your dive buddy is sloppy, or made the wrong decisions, had a less-than-enlightened instructor, then you’re making the wrong decision, too. Maybe you should get another dive buddy! The other issue is: cave diving equipment IS expensive. There is n