Look at it this way.... Will the OE one last four times longer (on the basis it costs four times as much) and is that within your tenure as owner? Mine has the Rimmer replacement which has worked perfectly for almost as long now as the original one did.
I bought a "genuine Lucas" switch from Paddocks a couple of months ago, seems fine it was around £30 if i remember correctly, there was the blue box version for around 2/3 the price. I wouldn't pay Land Rovers £140
I take it that it's for the defender in your profile if so should be part number prc3875. Lrdirect.com have them for as little as £12 or Lucas OE for £34