How much is a 1968 Proof Krugerrand worth?

As the value of bullion Krugerrand coins is very much tied to the price of gold it is difficult to determine the price of a 1968 Proof Krugerrand. However, a good estimate for a 1968 double frosted Proof Krugerrand would be about 110% of the gold price. The single frosted Proof Krugerrand is worth around 250%.
On the 29 May 2016 a 1968 PR66 Double Frosted Proof Krugerrand was sold on ebay for US$ 2035 which would be around 152% of the gold price.