There was a small run of this miscard, but with the Vader/Luke Jedi combo it is very desirable.
I'd say its probably a £150-250 value, but as Mini99 says, an auction maybe the only way to determine the true value. Many of the miscards going crazy right now are Vintage Collection ones. They have a huge following in their own right, with some figures demanding real Vintage prices, and the miscards are in another league compared to other lines.