It can be said, that this is a bit of an objective decision. In the case of climbing Everest which is classed as a hard adventure activity the cost of the permit alone was US$11,000 in 2015. Obviously, on top of that there is training, airfares, specialist equipment, tour guides et cetera. All of this brings the cost to roundabout $50,000 per person per climb
Commercial adventure travel tour operators offered soft adventure activities at a cost of $308 per day in 2012. The average length of the trip was 8.8 days bringing the cost to $2710 exclusive of flights.
One of the things that makes adventure tourism interesting is that it tends to produce really passionate people. So let's say someone goes onto a cycling holiday for the first time they will become more proficient and they are very likely if they enjoy to pursue the same activity trip after trip. The same goes for kayaking, caving climbing and fishing.
Another aspect that makes this interesting as a niche is the fact that they value highly specialised brands and equipment. They have specialist needs and are prepared to pay for them. They search for upcoming but not yet popular areas. For instance I went diving in Eritrea in the early 80s when no one and I mean no one went to Ethiopia on holiday, let alone dive.
Adventure tourism is big in Alaska, as you might guess. For a number of years, Kodiak fought the tourism explosion, but then were sucked in.
Cruise ships arrive regularly. Companies offering adventure trips do well. I got in on the edge of that industry for a couple of years. Had a business called "Backwoods Botany." Taught people about wild plants and took them on plant ID hikes. For two years, I took groups of young people from the "Semester at Sea" ship on plant hikes; gathered plants in plant presses; then they learned the actual biology parts when they were back on the ship. It wasn't really dangerous, but was an adventure.