Why would you buy a horse just to lease it out? If your thinking your going to make money on it, you wont. Most people who lease, either can afford the care all by themselves or don't have the time for it.
Most of the leases around here are free, if its an exceptional horse they may get the board out of it, but that is a rare.
I've leased before, but it was more of a sale on a payment plan...
I leased one out before too, it was a nightmare. I would lease again, but only under my care.
It's not something you'll make money at. People mostly do it so that they can keep ownership of the horse without losing money (or at least as much as they were).
Why bother to buy another horse just to lease him out? Around here, there are actually a lot of free leases, where you take the horse off of the owners property and then have to pay for board at the barn of your choosing.
For your average everyday horse, you are not going to make money.