Boost Mobile Website. Unfortunately there's no word on when Boost will be getting Apple's latest or what the price will be. The Learn More button on the site just takes you to a bunch of Apple supplied promotional material.
Historically Boost Mobile has priced its new iPhones at $100 less than full retail. If that pattern follows, Boost's iPhone 6 16GB model will come in at $549, with the 64GB and 128GB models priced at $649 and $749 respectively.
As for the date, last year Boost got the new iPhone Nov 8, 49 days after the postpaid and Apple Store launch. But Boost stablemate Virgin Mobile got the iPhone 5s on Oct 1, only 11 days after postpaid. It looks like Sprint is giving Boost all the love this year, as there's no mention of the iPhone 6 on the Virgin Mobile site yet. The iPhone 6 went on sale on postpaid on Sept 19 this year, so I'm guessing that we could see the iPhone 6 on Boost as soon as Sept 30, 11 days after the 19th.