Shouldn't your buyer be seeing the price in GBP? Perhaps it's Ebay's exchange rate?

Alternatively, I believe that Ebay started adding applicable taxes/VAT some time ago. Previously, buyers in the UK would have had to pay it before receipt of the physical parcel, but now it's included.

It will be easier to see once the transaction takes place as you can refer to the order details for the breakdown. 

Either way, my suggestion is that when you send it, you put a copy of the paperwork on the outside of the parcel. I usually fold it up and put into a small ziplock baggie which is taped down on 3 sides. Customs can therefore look at the receipt and ascertain that duties have been paid.