Well lets look at what a supernatural motorcycle could give a player, over what mundane equivalents would offer. Offhand I can think of:
-Mobility: Can Drive on walls/water/etc
-Flight: Can ignore gravity entirely, and move freely in 3 dimensions. Movement rate, maneuverability, etc is otherwise unchanged.
-Travel: Has a high Top Speed and Endurance, or some other mechanism (NN travel, time dilation, etc) to facilitate speedy long distance travel
-Maneuverability: Has increased Speed and Handling, making it more maneuverable than a mundane bike. Enough to make it useful in combat situations
-Offensive ranged Attack: Comparable to a Shotgun, so cost would be based on that as a benchmark
-Availability: The bike makes itself available within reason, but through supernatural means (IE is it always outside and waiting for you whenever you need it, comes when you whistle, etc)
-Summonable: The bike can appear out of thin air, even in the middle of a courtroom or a fall from an airplane.
-Stealth: Can operate silently, for the stalking of prey.
-Camouflage: Offers supernatural veiling function of some degree.
-Non-traditional Consumables: Does not require Gas or Ammo, but has some other basic needs that must be provided for (ie. Must be turned loose to hunt the weak and feeble prius’s/prius’/Prii? [Damn Correspondence Course], is powered by moonlight and must bath in it, or must be struck by lightning once a month, etc)
-No Consumables: Does not require gas/ammo/feeding to function.
-Sentience: Has some level of intelligence, from basic animal instinct, to a limited ability to understand basic spoken instructions, to full-on Knight-Rider talking vehicle with snark.
And from there you tweak the other limitations. Can you loose control of it? How long does it take to activate/invoke/summon? How long can you keep it active? Is it obviously Supernatural, so it will cause a stir in public?