Lease prices can vary all over the map.I agree with oakview, in that it may depend on the relationship you have with a friend or neighbour. It may be very worthwhile, to be reasonable if it is a neighbour who you want to have a good relationship with.
The person with only a handfull of cows is in a real dilemma as it is not really cost effective for them to purchase a bull, as well as maintain them for the entire year.
I used to lease a few bulls but I found there was too much variation in how they came back and some were so thin that it was hard to get them back in shape to even send them to market, let alone sell them as two year olds. I do lease one bull out each year, to a neighbour, and I get the use of his Bobcat any time I want it during the year. He has 8-10 cows and usually the bull comes back in better shape than he left here. This works well for each of us. We have an arrangement that if someone comes along and wants to buy the bull I am keeping for him, that I sell it, but I also pull some of my own bulls in late July, so has agreed to use one of them.
I know another family provide a bull to a neighbour for some baling, or backhoe work, and again, the bull is only exposed to a few cows. I know of another situation where a bull is supplied for the use of a 5th wheel camper is provided for 10 days.
I do not think in this day of everything costing a lot of money, that $50. cow is unreasonable. You can maybe drop that a little if they agree to keep the bull for a few weeks after they are done using him and feed him a little grain to regain his condition. There are lots of options.