I would say $550 top and only if the GIA does not show the I3 clarity grade. I definitely would not pay to have it graded especially as it looks a lot more brown than yellow and may be a fancy yellow brown rather than a fancy brownish yellow. If it was mine I would keep it and have it set and wear as a pendant rather than waste more money on it, try to sell but keep if I couldn't get more. Probably just end up keeping it and set it with fire opal or amethyst.