Even if they charged $0.50/per user, that would be $5k/month. I could go as a consultant and charge half of that to setup vaultwarden integrated with their AD for maybe 2 lazy days, and offer a support contract for $500/month. It's not even that much of rare skill. I'd guess you can randomly selected /r/selfhosted users and I'd give 10% of odds to find someone who has done it already and would even offer to do for less.
Yet, I think that most managers would simply prefer to go through all the negotiation meetings, all the internal procurement process just so they can justify the big boy expenses.