The typical half lease price is half your monthly expenses, give or take a bit.
Realise that for a “very experienced” rider, a safe but green horse is not really that much fun.
You only ride 4 times a month? Once a week? Is he in a full time training program or just sitting in a field?
At our barn there are basically three ways to get riders on your horse.
One is the leaser pays you. This works when you have a horse that the average rider can enjoy. Often these leases stipulate the leaser has to take lessons with the owners coach. Typically these charge a per cent of monthly costs. Our barn is inexpensive so a typical half lease is $200 to $250.
Another is, you pay a trainer to ride your horse, generally your coach. Our trainers are all very small time so I’d expect about $30 a ride.
Then there is a third category. Right now I can think of one adult (horseless) and one junior (with flexible time, homeschooled) that fall in this category. They ride well enough that people know they will improve the horse. But they haven’t fully professionalized and don’t make any promises about actually teaching your horse anything on a timeline. These people ride for free. They don’t charge, but they aren’t willing to pay to lease your horse either. There aren’t that many people that fit this category, since most of the better ammie riders at our barn have their own horse and not a lot of time for other people’s horses.
So I would say in general if you want an experienced rider to improve your green horse then you pay them.