We rented a bull last year and paid $20 per cow bred. we ran him on roughly 30-40 head of purebreds so 600-800 for the breeding season. Seemed as reasonable to us, but based on the bull you could probably raise or lower the price.
I charge 20/cow/month. The leasor is responsible for care, facilities, and 50% of bull value if the bull is injured or dies. Bull must be returned in good shape. No charge for junior projects other than care and insurance.
Quality bulls are worth a minimum of $4,000 here now and the only limit is your pocketbook. I wouldn't let one of my good bulls leave my yard for less than $1,000 per month. Not worth the risk otherwise. Plus the leasee would need to insure the bull for full value.
I agree with nyk that the leases will need to carry full insurance on the bull. Especially in this current market where the bulls start at $4000 and quickly go up. In the case of juniors I would offer to bring their cow into our program to get covered free of charge.
Good point diamonddls, I absolutely have and will offer to let local juniors bring a heifer or two to breed to my herd bulls. I'd much prefer to pasture a couple extra head than risk injury to a valuable bull.