The monthly cost per hardware unit is the cost coming from leasing a unit via Velory (leasing agreements ordered outside Velory are thus not stated in the monthly cost). When units are leased, a residual value is calculated which is guaranteed at the end of the leasing period. The leasing period is usually 24 or 36 months.
The price per month is based on the decrease in value during the period in which the unit is used. This means that you as a customer only pay for the device during the time period it is used. It also means that the monthly cost is lower when the leasing period is longer.
The total monthly cost for the company's leased products is available in the overview. You can also go to the statistics overview to see the average cost per type of unit in the company.