Interesting question. Are you referring to the filament costs if you build it yourself, or the cost if you send it out to a printing company to make? I have never used a printing company so I couldn't give any guidance there.
As with any home based 3D printing project, if you have the colors you want already on hand, then I guess to say that all the filament used for the full project is less than a quarter of a spool (1/4kg). Figuring $25USD per spool, that would be $6.25. In my case I needed to buy one of the colors and had the other ones already on hand.
Hope that helps a bit.