The barn where I was taking lessons offered me the opporutnity to lease a horse with option to buy. My issue is that I can't afford the full board yet. For $200 a month I get unlimited use of a lovely little buckskin or an arab/appy cross. I coordinate with the barn manager when I am coming and we make sure the horse I want to ride is not overworked. It works out very well. I also pay $35 every other month for the farrier and up to $100 per YEAR in vet expenses. They cover all other costs and have the option to use him as needed for lessons or trail rides. It helps them during the winter months, they have fewer lessons, and my money essentially pays his hay/grain bills.
I can exercise my option to buy at any time with a contract for a year's board. This is useful to me because these horses are for sale, if they get a potential buyer, I have first refusal.