Tubac-- the price varies, depending on who does the work, and what they have on hand for material. Going rates for real ivory are in the $400 - $600 range. Fake Ivory (plastic) such as Tru-Ivory, around $250. The cheap polymers are in the $50 - $100 range. I chose to go with the real deal-- couldn't see paying up to $250 for fake ivory when the real deal is not a lot more.
USFA lists optional grips on their website, you can order from them, Nutmeg Sports I can highly recommend, I believe Elen Hunting has some, You can try and google on Ivory Grips.