The official report from EVE Online developer CCP on what it calls "gaming's most destructive battle ever" estimates damages at 11 Trillion in the game's currency (ISK), which equals approximately $300,000-$330,000 USD.
The conversion rate is based on players' ability to use ISK to buy PLEX, which they can then use to pay the game's subscription fee.
More than 75 Titan class ships were destroyed in the battle, each valued at about 100 billion ISK, which would equate to around $3000 each. They are the largest ship class in EVE and take thousands of man hours to produce. Up until now, no more than 12 Titans had ever been lost in a single battle.
And it all started because of one unpaid bill. "In the early hours of January 27th, 2014 CONCORD (the NPC 'police force') came to collect the sovereignty bill for a dead-end system in the Immensea region called B-R5RB," CCP wrote on its website. The system had recently been transferred to a player corporation called H A V O C, used by the alliance Pandemic Legion. For some reason, H A V O C forgot to set its automatic payment, meaning it didn't pay its bill and immediately lost control of the system, leaving it open to attack.
The CFC Alliance and Russian-heavy coalition forces seized the opportunity and started a battle which lasted 21 hours. 7,548 players participated in the fighting. The CFC eventually won the day, but with heavy losses, including 16 of its Titans destroyed.