For one day only, Buy via eBay is selling the retail version of Halo 3: ODST for just $39.99 shipped, originally priced at $59.99. This standalone expansion “contains 1,750 new Xbox LIVE achievement points, as well as new weapons, technology and an invite to join the Halo: Reach beta in 2010.” Product page.

All-new campaign content. The “Halo 3: ODST” campaign is an intriguing side story that takes place during the terrifying events leading up to the Master Chief’s return to New Mombasa in “Halo 3.”

[via eBay]