You generally pay $25-30 a ride for a mediocre lease horse. So you pay $100 a month to lease one day a week, $200 for 2 days a week, and so on. However, some barns have you pay half of the horse’s expenses per month as the fee instead. This is for a half lease.
For full leasing, it depends on if it is a free lease or not. Free lease means that you are 100% responsible for ALL of the horse’s expenses(board, farrier, vet, training, tack, shows, etc) unless stated otherwise in the contract. Also, there is another type of full leasing seen commonly in the hunter/jumper world in which you are responsible for all of the horse’s expenses, but you also pay a lease fee on top of all of it(in h/j land it is 1/3 of the horse’s sale price). So, for example, you could pay 25k a year as a lease fee and also pay for all of the horse’s expenses.