A couple of approaches:
1. Work with one of the FCC approved frequency coordinators to find a suitable frequency you can use. Then get licensed for the frequency from the FCC. Then purchase radios. To cover all that area, you'll need to spend a lot of money on repeater systems, linking, etc. Very expensive approach and a lot of money in upkeep/maintenance, radio sites, etc.
2. Work with a radio shop that already has coverage in the areas you need. Licensing is handled by the shop. You'll pay for radios, plus monthly access fees. Less up front costs, but ongoing monthly fees. You won't be able to add your own radios to their system, you'll need to buy radios from them and have them program to work on their system.
3. Try to cobble together your own system with license by rule services (MURS). Headaches will persist, in the end you'll probably end up buying service from someone else.
4. Try one of the newer LTE radios that will work over the existing cellular networks. Wide area coverage (Nationwide), infrastructure costs are covered by the cellular carriers. You just buy the radios and put in the cell carriers SIM card.
Icom makes some small radios that will do this:
LTE Radio Solution - LTE-CONNECT - Icom America
If I was in your shoes, I'd go with the LTE solution. Much cheaper in the long run, much more flexible. Easy to add radios. Much better coverage. Actually would provide some level of security.