In an interview with Dean Hall, creator of the DayZ standalone zombie survival game, he spoke of the pricing model used for the now closed alpha stage of the game's development.
Until the game reaches the alpha stage not earlier than June, DayZ will not release. Once the transition to servers occurs, they will review the game's status in June. Following that review, an alpha phase similar to Minecraft will allow people to pay set amounts at each stage of development. People who purchase early access will pay the lowest entry price and those who wait until the full release or for the beta stage, will pay an increased price.
"People pay X amount of dollars and they get early, cheap access to it, and then once it's beta, price goes up, maybe, say, $10, and once it goes retail, the price goes up $10."
As a gift to forum moderators, Reddit moderators and people who helped during DayZ's development, they will receive free keys to access the game which according to Dean Hall, estimates "about 30-100 people."
DayZ first started as an Arma 2 mod and later exploded in popularity within the Arma community and even spiked sales of Arma 2 on Steam. The developers on DayZ first announced its 2012 release but it was pushed back multiple times.