Not sure if this is old or what but Xbox twitter posted it and I figured it was worth posting anyway. Far Cry 3: Blood Dragon (no it's not an add-on to FC3) is available at HALF PRICE for Gold members. So it's £4.99/$7.49/€7.19 instead of it's usual price.
http://marketplace.xbox.com/Product/Far-Cry-3-Blood-Dragon/66acd000-77fe-1000-9115-d802584113bf