This Is what I think that I would do.
You have the cows, he has the contacts.
Around here, it costs me 800 to 1,500 to flush a cow. That includes everything. Including board. The variance in price is due to the number of embryos that are to be frozen. That is where it will be a "cost per embryo" expense. There is no way to know how many #1 and #2 embryos you will get to freeze.
I personally would partner with him. I would have a contract that would give him a certain percent paid in $ or embryos of what he sells. The two of you need to determine the sale price of the Embryos. All payment comes to you, and then you pay him his commission. I would take my cows to a reputable Embryologist or a vet that specializes in flushes. I would have the agreement in writing, and maintain control of the cows and embryos. The Embryos stay with the vet, in his/her care for a modest storage fee. (There will be shipping costs added to the buyer.) The vet does all of the shipping for you.
I would start off with just doing one cow, and see if he gets those embryos sold and money in hand, before I invested any more money into it.
My :2cents: