I think one of the cool things about larp in general is that you really can choose how much you want to spend. You can choose whether to shell out for a fancy sword from overseas or to borrow one from a friend for the weekend. You can choose whether to buy some nice, genuine looking medieval garb from an artisan or to spend an afternoon opshopping. You can choose whether to buy an old in-character looking tent or to take the modern one you already have.
My only other real hobby is music, and so far that’s definitely been more expensive. At one end you’re buying instruments, equipment, consumables, maintenance, and software, and at the other you’re buying cds and merch and tickets to the bands you’re into. Playing and/or producing music tends to be particularly expensive, especially if you’re looking at instruments other than guitar/bass/drums. I’d be paying several thousand dollars for a decent upright piano, about twelve thousand for a cheap baby grand, and about half a million for the piano I really want - whereas all of my guitars have been under about six hundred and the two I use now come in under five hundred combined.
To an extent there are similar options to those above - I could borrow a keytar for a gig; I could pick up a much cheaper violin at a second hand instrument store; I could wring another week out of a reed rather than replace it when I’d prefer to. I think these sort of options probably exist for a lot of hobbies.
So, I think larp can be expensive, and probably is more expensive than a lot of other hobbies, but it depends a great deal on how it is approached and managed.