Marathon

The game is sold for roughly 40 USD and offers a Deluxe edition for an additional 20 USD. This grants access to one premium Battle Pass track, 200 premium currency (which is not enough to purchase any items in the store), and a set of unique weapon and character cosmetics.

Battle Pass

Marathon releases a new season season every 3 months. Each of these will contain a Reward Pass, which is a battle-pass like reward track. The pass contains a free and a premium track.
The "SILK" currency is unlocked through gameplay and is used to unlock items in the Reward Pass. This currency has a maximum amount you can carry at one time. If you are at that maximum without spending you will not earn more.
Each Reward Pass will contain roughly 50 unlockable items. All of these items are cosmetic only.
Reward Passes do not expire with time. Once the season is over you will continue to be able to both unlock items in the pass you have already purchased, and purchase other passes you may have missed out on previously.

Premium Store

The game contains a premium currency called "LUX". This can be purchased in inconvenient bundles where 1000 LUX equals roughly 10 USD. Bundles are sized as 500, 1100, 2250, 3950, 5750, and 12000 LUX. This currency can be spend in a premium store on cosmetics items that only come in packs. These packs feature discounts despite the items not being available separately. The discount is supposed to indicate the price savings compared to purchasing items individually, but purchasing them individually is not an option. These discounts also do not lower the actual purchase cost needed if you do not wish to purchase multiple LUX bundles. For instance, packs may be discounted from 2100 LUX to 1500 LUX, both requiring the 2250 LUX bundle to obtain enough currency. Alternatively you could purchase two bundles at 1100 and 500 LUX, which will still leave you with 100 LUX left over.