Have you joined STEP? It's Burner to Burner ticket sales. It's a long line, but you may get lucky (there, or through other means).http://tickets2.burningman.com/faq.php#step
There's also a last minute "OMG" sale.
Tell everyone you know you're looking--friends, family, co-workers. Plan as though you're going to go---read the Survival Guide linked below--several times, get your time off, save your money, make your shopping lists. Last year in August, the tickets from flooding out of the woodwork at face price and sometimes below. Those who were ready got to go.