"Pedro Popadopolous" wrote
Has anyone any idea to help me start negotiating?

Price per acre?

Depends on location, on how much it will add to your property and detract
from his.

Whatever you pay, and it will depend on the location, don't forget there
will be solicitors fees involved + Land registry fees so take the cost of
that into account as the seller will, no doubt, expect you to pay all fees.

--
Regards
Bob
In Runnymede, 17 miles West of London