The cost is high due to basic economics. The BLM permit doesn't allow them to let in as many people as now want to come. When they charged a "reasonable" price

The cost is high due to basic economics. The BLM permit doesn't allow them to let in as many people as now want to come. When they charged a "reasonable" price all the tickets got bought up instantly and people complained about not being able to get in without paying a ridiculous markup to scalpers. Rather than let resellers reap all the benefit of their event, they charged more the next year (especially for last-minute purchases, which complicate planning) and still sold out. So they kept raising the prices until most of the excess demand had been soaked up. Now people who care a LOT about going to BM pay a high price and/or book early, people who care less are dissuaded by too-high prices, and demand more-or-less matches supply. The extra income means they can spend a bit more on artistic grants to make the event somewhat more worth the high price...and also bump salaries and profits a bit.