To buy new, each of the sided parts is around £58 inc (I've just done my O/S!). I reckon at Nissan prices, the centre part would be £35 inc.
However, as yours are Blueprint/not original Nissan (although, you can put money on the fact that they're made in the same factory as the Nissan parts !) they'll probably be worth a quarter to a third less, as they didn't cost as much to buy !
Ultimately though, they're only really worth as much as a buyer is willing to pay for them !
Out of curiosity, where did you get them from ?