With a press release today, the software company VALVe has confirmed that the upcoming game DotA 2 will be free to play and wrote some details about the upcoming Dota Store.

Valve, today confirmed that Dota 2 will be free to play and announced the Dota Store in preparation for the game's release. Upon its opening, the Dota Store will offer items created by Valve and members of the community. Early Access to the game is not required to purchase this items before launch.
The best thing is, gamers who have no access are now able to get into the game by purchasing the Dota 2 Early Access Bundle of items. "The opening of the Dota Store is a big part of our final push to launch," said IceFrog, design lead on Dota 2. As VALVe announced, the game is targeted for full release on the PC later this year.
Source: Press release