If there is only 1 on the market than 66 666 666. I would say for collectors around 1,000-5,000 if very bad card or you just don't want it. . 6,000,00 - 10,000 if it is ok. 10,000 - 5,000,000 if it is good or really good but not great. 5,000,000 + if it is a great card. But not more than 10,000,000. But if there is only 1 that you know of and you have it sell for a couple of ten million.
A hint of advice: Most people don't go around with 1 000 000's of clintz unless they are saving up for something special!!!