From the Main Sale FAQ:
Q: Will I possibly end up buying a ticket at a pricing tier I can’t afford?
A: No. During registration, you’re able to specify the highest pricing tier you wish to be considered for.
Q: How do I increase my chances of getting a ticket in the Main Sale?
A: You can increase your chances by opting into all the pricing tiers. (We believe, based on many years of analyzing supply and demand, that most participants will find they are able to access a ticket on an acceptable timeline.)
Burning Man 2003-15; Desert Carillon, HypnoHorse, Ulaume's Chimes, Iron Native, Black Rock Solar, Portal Collective, Center Camp Café Stage and Sound Tech