In ,
Pedro Popadopolous whispered softly in my ear...:
Has anyone any idea to help me start negotiating?

Price per acre?

Depending on the circumstances, there may be bigger concerns than price
to negotiate.
We have sold some of our large-ish garden to a neighbour. We did not
need / require such a large garden so, in theory, the sale was a good
idea for both parties. The price agreed was reasonable and was, in fact,
the original offer the neighbour made ( in other words what it was worth
to him and what he could afford) The only negotiating involved was to
satisfy our concerns that , at some future date another neighbour would
sell part of their garden and the combined area would then be big enough
for someone to use as a building plot. Whilst I don't want a big garden,
I don't want a new house at the bottom it. We got round the possibility
by means of a complicated ( but legally binding) agreement which our
neighbour was happy with.

--
Ticketty᧧