Lumia 830 comes with free Fitbit Flex offer and is priced $99 on 2-year contract.
*Nokia Lumia 830/Fitbit® Flex™ Wristband Offer: Offer ends 1/8/15 or while supplies last. May require activation of Lumia 830 w/qualified voice and data plans. Includes black Fitbit Flex wristband bundled in box only. Excludes Fitbit Flex wearable in other colors and Fitbit wearables sold separately.
HTC One M8 for Windows is priced $199 on 2-year contract.
You can read our unparalleled coverage of Lumia 830 at its dedicated page.