My guess is he has $15,000 into the system. Giant solar panels and the wind turbines are about a grand each installed. Payback has to stink. Guy just hates the power company. BTW I cannot tell you how many hours he has tinkering with the system - it is large. Guess it is more of a hobby.
That seems like a pretty low ball figure unless he installed it all 20 years ago.
I would expect a system you describe to take a house off the grid to run around $50 to 75,000 if you do much of the work yourself and around $100,000 if you hire it out.