So, like Project25_MASTR, I run a trunked system. It's for a large agency, but large agencies are like small cities, so it translates pretty well.
I figure I put about $300K into my system. I was able to reuse some items left over from the old system (tower, feedline, etc), but $300K resulted in a new site.
That's a lot of money.
Scale it down to one repeater, like a small business would use, that's still a heck of a lot of money for Joe-Bob's plumbing service.
So, take Joe-Bob's plumbing, Billy Joe's towing, and 20-30 other small businesses with catchy names and each one needs to put up a single repeater. That's a few million in equipment, radio sites, etc. Most of those repeaters are not being used at any given time. They are sitting idle until Cletus needs a new left handed toilet flange. Then a minute or two of traffic, then nothing...
Or take a trunked system, Take 6-7 repeaters, hook them up to a trunk controller. Give those 30+ business a talk group on the system. Now instead of a million or so bucks in repeaters, Matt's repeater service sunk $300K into the trunked system. He sells each company a talkgroup (or two) on the system at $12.50/radio per month. Oh, and that same guy sells them the radios.
Now each company gets what they need without the huge upfront investment and ongoing maintenance. Those costs are spread amongst 30+ companies. Due to the nature of the trunked system and channel loading, each company thinks they have their very own private radio system. But those of us in the know understand that we're just reselling the unused airtime to a bunch of different users and laughing all the way to the bank. (not really…)
So, a trunked system just spreads the cost around to a lot of users. The channel loading calculations make it so 99.99% of the time, the system has free space to support a user. Periodically (a few times a year) someone keys up and gets bonked because there is no repeater available. Wait 5 seconds for a user to unkey, and it's freed up.
So, my $300K spread across 450+ users with each radio paying about $12.50/month covers all my costs, salary, electricity, spare parts, emergency repairs, cold beer, etc.
And each of those companies is happy that they don't have to pay $100K + for their own repeater, plus all the costs of upkeep, repairs, electricity, deal with licenses, etc. They get to spread that $12.50 a month out and it's not such a big investment.
Of course, as others have pointed out, cellular has taken a HUGE bite out of those systems. Most people don't want to carry a radio around when they can do essentially the same thing on their cell phone. And who can blame them. 99.9% of the time, the cellular system works just fine, and has way better coverage than a trunked radio system will for most users. The costs are cheaper, plus you can play angry birds on your phone, but not on your radio.
The benefit to the trunked system is that it can be designed to be more reliable than a cellular system. It can provide coverage into areas where the cell carriers think there are not enough users to justify the cost of building out a cell site. And you can control access to you limit access to just those that need access, and not every kid with an iPhone trying to stream Tic-Tok videos.
The truth is that as cellular systems grow and there's more and more bandwidth, they are a much better solution for many non-public safety users. You can do a lot more with a cell phone than you can with a radio, and the costs of the infrastructure get spread out across more and more people.
Your milage may vary, void where prohibited, not valid in some states, and sure to piss someone off.
