Actually, not exactly a rave. And apparently always been a gift-economy. See the great documentary GiftingIt for more details on this. Very interesting.
The burning man itself (a humanlike figure that gets burned) is a kind of modern, imagined ritual. Nevertheless, the ritual starts getting interpreted by those involved. Artists burn their work at the end of the festival in a kind of ceremonial PotLatch. People burn items in memory of lost loved ones.
The BurningMan people think gifting creates community. And trade destroys it. Hence they "draw a circle in the sand" within which commerce / trade / exchange isn't allowed. Some barter occurs informally, but by and large gift-giving is the greater part of the economy. For example, one group raised 6000 dollars to buy water and take it to the festival to give away (in the middle of the desert).
OTOH coffee and tea are available for purchase : http://eplaya.burningman.com/viewtopic.php?t=4488
Survival guide : http://www.burningman.com/preparation/event_survival/index.html
: a lot of rules. Necessary, of course. (Compare CreatingCommunities)
Increasingly expensive and well funded art projects are always controversial : https://www.theguardian.com/culture/2017/may/18/burning-man-plane-art-boeing-747-ken-feldman