A lease is a long-term contract with specific commitments. From what you describe, you would be responsible to continue to provide a fully functional system for the duration of the lease.
For multiple reasons, you will probably want to structure it as a $1 buyout lease, unless you really want the equipment back at the end of the lease term.
So, to get to your lease price you would need to factor in:
Add those up, divide by the number of months in the lease (probably 36-48), and that is the monthly payment the customer would make.
Though you did not ask this, for the same thing as a rental you would typically divide by 30-60 (days) to get to a daily or monthly payment. The reason you charge so much more for rental vs. lease is because for equipment that is rented you do not have the long-term guarantee up front, and the equipment generally goes through more wear and tear from setup/delivery and removal, which incurs more support and repair costs. Once you rent the products once, they can no longer be sold as new, and will sit on your shelf for an indefinite amount of time, so you have to charge more to make up for that.
If you know upfront that your rental offering is going to be high demand, and/or low wear, you can divide the costs by 180 or 360. It takes you longer to recoup your investment, but your risk is lowered so you can take a lower price.