a "contract" is "a meeting of two or more minds in agreement"...
doesn't even require a handshake.

What you are obligated to is the amount of work you told this guy to do
before he took off. There is no question that what he did while you
weren't aroung, and without asking, was not part of the original
agreement nor warranted in any way.

You did not ask him to do an additional $1100 worth of work, plain and
simple... When an electrician comes out and says "I'll wire up that
outlet for $20" then you *technically* arent obligated to pay $20.50 if
he wants to charge you for wire nuts or something.

Get a lawyer for cryin out loud. This has been answered fifteen times
by amatures and tradespeople alike in this forum.