Most of the time (probably all), I've leased rams only to people that have previously purchased sheep from me. As a general rule, if someone buys a ewe lamb from me in and only has sheep from me, I will offer to let them bring the ewe lamb back to get bred for free that fall. It's not uncommon for them to then in year 2 ask if they could lease a ram. If we are leasing a ram that's likely to sire decent show lambs, we start at $50/ewe. If it's a ram with a more commercial orientation then we start at $35/ewe. If it's a ram that's worth more than $1,000 we have the discussion about what happens if he should die. If I lease a ram that I'm done with and was planning to ship I don't worry that much about it as the lease fee they've paid is probably already more than what he'd bring as a slaughter ram.
It's usually small flocks that want to lease my rams and since they've paid decent money for ewes from me I try to help them out by letting them have access to decent rams at a reasonable price. If they stay in it long enough I then may propose that they buy a new ram jointly with me.
With our NSIP side of our program, having the same ram used in multiple flocks is important to get the genetic links established. In those cases I've lent out rams to other flocks to get a better link. In the future if I do that, I will do it probably only in 2 conditions. One would be we are each swapping comparable rams that year. If not, I'd stipulate that the people using my rams couldn't sell any rams sired by my ram. I've found that invariably without that stipulation, lambs sired by my rams, or sons of my rams are offered at sales competing with my genetics.