I'd be inclined to tell him you are interested in expanding your work into large format if you could find a deal that would work for you . . . and also work for him, you would like to get started. I would probably then ask him, "What do you need for me to take this gear out of your home and put it in mine and start using it?"
You do need to know what he has.
My bet is Momma wants it out of her house. He wants it out of his house and it really isn't about the money. He would also like for someone to be using that which previously was his treasured equipment. Depending on what he has, I would agree that somewhere around the $500 mark could be a win/win and I'd ask him first what he needed before I made any kind of offer. If his needed number was in my comfort level, I'd agree to his price. You have to work with this guy. I don't feel obligated to negotiate a price when someone gives me one that I think is fair and in my comfort zone. I've bought and sold a bunch of photographic equipment over the past 10 or 12 years.