That said I can't help you much on price, in my meager experience, and in my area, palys don't tend to fetch huge prices or sell like hot cakes. . . but being grandis may change that?
Like MoshJosh said, definitely a beautiful piece, but hard to price. Most people prefer to pay the price for one polyp and let it grow out rather than spend the money on a larger colony (depending on the coral, of course).
that being said, most vendors online have Grandis for $40 for a couple polyps, so make of that what you will