Avatar (Xbox Live)
From Halopedia, the Halo wiki
Avatars are visual representations of users of the Xbox LIVE service on Xbox 360, Xbox One and Windows Phone. Avatars debuted on the Xbox 360 as part of the "New Xbox Experience" systems update released on November 19, 2008. Numerous Halo-themed items are available for avatars on Xbox Live. There are seven different types of items: tops, headwear, accessories, props, bottoms, shoes, and "dress up" (full set outfits). As of November 2011, avatar items can be purchased through Halo Waypoint.
Avatar Awards are accessories which are unlocked for completing a specific task in one of the Halo games or on Xbox LIVE.
Certain items are only available via pre-order, launch day purchase, or limited editions.
Numerous items are also available for purchase with Microsoft Points prior to August 23, 2013, and with local currency thereafter. All tops, save for the Firefight hoodie, cost USD $1 (80). In headwear, hats cost $1, helmets $1.99, and masks $2.99. Props cost $2.99 or $3.99 (save for the RvB Grifball which is only $1). Most full "dressup" outfits cost $3.99, though several cost only $2.99, and a few cost $4.99. The other three items are Corbulo Academy Pants & Boots and the Halo Cargo Shorts, both costing $1, and the Laser Kill Ring for $0.50. For the full catalogue with exact prices and additional currencies, see the Xbox Live Avatar Store.