A year or two in municipal government can be considered right around the corner, if you will. With ~100,000 population right now, it would be relatively simple to start a Fire Department and lease the comms. Arizona considers a town to be 3,000 in population and it can become a city with the adoption of 'home rule'. Somewhere, there are attorneys working on articles of incorporation, setting up a civil service, tax rates, insurance, and all the other busy work that a new municipality brings.
Rural-Metro is subscriber based and there are businesses and residents who will not pay for fire protection. As to policing, the California county model is not very popular here, with Gila Bend disbanding their PD in 1972-73 and Youngtown ending its' own PD in 2011. Fountain Hills never adopted a PD, but with 'Sheriff Joe' living in the town and with his executive protection detail, they had better policing than many other towns. Cave Creek had a Town Marshal for a time in the 1990s, but it was more of a Code Enforcement office than a LE agency.
With the size of the population of San Tan and the birth of Queen Creek PD, I can't see why residents would go to a County based agency for policing. Even Jerome, AZ with a population of <500 citizens has their own PD.
