How many is he willing to pay for?
If your not getting paid, then that question can only be answered by you. How many you want to haul over for nothing? 2 hives would be almost overkill for 150 trees.
Accounting for local beneficial pollinators, he may not even need honey bees. Your only talking about a 10x15 planting of trees. If he recognized the need for additional honey bees due to poor past pollination, I would question what is going on that there is so little native pollinators doing the job. 150 trees anywhere should almost never have pollination concerns unless something is impacting the native beneficial pollinators, like sprays and chemicals. Most orchards that need honey bees brought in usually number far more than 150 trees.
I would take about 10 myself even if he only paid for two. That way, my time and effort maintaining them, would be worth it by going out to another yard. That of course would be based on much more information of whether this site was even worthy of my bees being placed there. Most orchards and commercial places are not the best honey producing sites, and may have other issues.
I also do not do "migratory" beekeeping. I have some smaller yards, but they are year round sites. I use them for honey production or nuc building sites. All the hives are rented. You could not pay me enough to move bees in and out of orchards.