Arma 2 and Operation Arrowhead are now $19.99 each or $29.99 for Combined ops!
Expansions are $9.99 each
They have also added Arma: Cold War Assual and Arma: Gold edition
Next steam sale you might be able to grab Combined ops for around $20 or less, so keep an eye out
Hopefully there will be a sale before the Project Reality mod releases. Would be worth buying for the mod!
