To use the PERS cost calculator, simply input any initial cost (such as an up-front fee, cost to purchase the unit, etc.), the periodic rental cost or monitoring agreement cost, the length of time you expect to use the unit, and then click calculate. The calculator will display the cost per year, per month, or per day.
This should allow you to compare the costs of various PERS units (and monitoring service agreements) as well as to serve as a basis for budgeting for your future needs.