Its not rude to ask your tattooer for their rate. It is rude to ask various artists for prices on a design and price hunt. Show that you intent to get tattooed by the artist you want and ask for price once everything else is done.
I always ask how much the tattoo will be, but I do it last. If you hear artists complain, its from people who price hunt and dont really want a tattoo, they just want a deal.
Tattoo prices vary, based on so many different factors. Only the artist doing the tattoo can tell you how much a design will be.