I don't know anything about cost but thought it might be worth mentioning two things.
Temperatures: I'm not sure how well a powder based paint stands up to heat but normally there are specific paints designed for higher temperatures.
Decals: The other thing is I recently bought some new Brembo decals ready for mine being refurbed and in the instructions it mentioned specifically powder based coats as not being a great surface for them to stick to. Something to do with a residue being left with that type of paint?
Thought I'd mention those things in case you need to find out more. On the flip side I know there are advantages to using powder paints so I guess its just a case of weighing it all up.