You can try VR Mocap Studio for free. Using evaluation version, you can't save captured animations on disk, and duration of exported animations is limited to 15 seconds. You can always update your evaluation version to full version.
VR Mocap Studio package provides license key for the software. Read EULA and more about Advanced support in the documentation. Unreal Engine 4 Plugin includes access to ViveMocapKit plugin for at least three last stables releases of the UE4. You can buy UE4 plugin separately at Unreal Marketplace ($139,00).
The only available payment method currently is PayPal.
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