Andy suggest:

Here's and idea. Put in a second pump for yourself. Tell your
neighbor that he can have the "old" system as his own, but he
will have to put in his own electric line. That way two pumps
will use the same suction line (not a problem with a check valve)
and the expense to do these items will be roughly the same.

If the neighbor doesn't go for it, ask him what he would suggest
as a fair division of the costs of providing water to you both.....

By the way, whose land does the suction line exist on ?
If you two reach and agreement, be sure that an easement
is provided to the suction line, or anything that is necessary
for the operation of the system.

Sometimes it's better to bend a little than to insist on what
one feels is one's "just" rights. A good neighbor is far more
of an asset than an old pump....

Andy in Eureka, Texas