Fuzzy, I'm thinking you are high in your expectations having recently just disposed of most a collection I bought of 750 records. I got them in spring, sold the high value records I was planning on selling within the first month, and that paid for my initial investment. Those were mainly great first pressings of desirable classic rock, metal, and hard rock. There were lots of others, but they are the type people pick up in record stores. My prices are now at $2 apiece for the last 180 of them and I kept about 300. It has taken me until now to sell the others at average about $4 each. I will likely set the remainder at $1 each and there is still some good stuff in there! After another month, these are going to the thrift. And this was a good collection!
So figure you will get greater than $5 on maybe 30% of the collection depending on the distribution. It could be less, but isn't likely to be more. And you are going to have to work at it. It will take a lot of the fun out of it if you need to recoup someone else's money and turn it into profit.
Just saying...
Edit: I agree, this is a flipper. And the 50k is the starting point of the discussion. Going there with a good chunk of change more than he paid for it will do wonders In negotiating, if you do decide to go.