Can anyone tell me a reasonable price to pay for a pair of D2 facelift head lights ? they seem to range so much in price

I would think it depends on if you require new or used.
Using a respected Land Rover parts supplier for a new genuine part or used parts from an eBay or a similar seller selling something of doubtful quality, broken retaining clips for example could mean the unit has been forcibly removed from vehicle I believe, possibly in the early hours of the morning
As always with eBay prices will be variable, but you could look for the units at a local LR breakers.
The bottom line Is what u think is reasonable. I think Rimmer Bros prices are reasonable for genuine parts.