As Raffe points out, what the dealer will pay for the strap is VERY different what he would pay.
Surely an accommodation where the dealer offered you a new strap at cost to him could have been reached? I'm guessing it'd more like £100-150 or so judging by the price o the public of a Camille Fournet croc at £180-200 or so (resold with a JLC stamp for £300).