CDKeys offers downloads of Alan Wake for Xbox 360 for $5.19. (It's also backwards compatible with Xbox One.) That's the only vendor currently offering this soon-to-be retired game, although we saw it for $3 less last year.
Note: New customers can provide an email address on the CDKeys Facebook page to get a unique coupon code that cuts an extra 5% off. You can also download The Writer and The Signal DLC for free via Xbox Live.