The original applications are available for these auctions, and Automattic's application says they'll utilize a pricing structure that's less than $15 per year for the new domains:
For the first five years of operation of the .BLOG registry there will be no price increases. No one year term of registration or renewal will be higher than 15 USD as per our pricing strategy.
The application notes that they will likely use a discounted pricing system for the first year of registration. They also anticipate they'll, “be the domain extension of the address of 150,000 blogs,” within three years.
The application says they'll reserve one and two letter domains, “as allowed by ICANN policies,” which is a bummer for my hopes of reserving bk.blog. I hope I can at least settle for krogs.blog though. Finally, other “premium” domains will also have higher prices, which is a common practice for the new gTLDs.
The .blog extension is a logical one for Automattic to go after. They will surely be able to promote the extension heavily from WordPress.com and Jetpack. The ROI will take years, but as long as the new gTLDs are a thing for the long haul (which is highly likely, I hope) then it will eventually be quite the cash cow, especially because it's such a pronounceable extension that helps instantly identify the site's purpose.
Automattic applied for the gTLD in a stealthy manner, which is sensible in this case, as knowledge of your bidding competition wouldn't be ideal. WP Tavern reports that they're partnering with Nominet to manage the extension, which is a change from the original application, which cites Qinetics.
If you have a trademark for your brand, you can apply for your trademark domain in August, otherwise there's a “landrush” application period in October, and general availability in November. The landing page on WordPress.com has more details, and a way to sign up for updates on when you can apply.