Welcome,
There's a lot of details you need to consider. There are legal/licensing issues that need to be taken into account. I'm going to add one line to your list based on U.S. rules, if you are not in the USA, rules will vary slightly:
* Waterproof/Water-resistant
* Programmable in the 154-156 VHF range
* Dual Watch or reliable scan mode
* Programmable with free included software (or Chirp)
* Must have valid FCC Part 90 certification
The FCC issued license for your agency comes with some very clear rules that must be met. There is no waiver for these rules. Lack of budget, volunteer status, location, etc, all doesn't matter, the FCC license binds you to these rules and it is absolutely, 100% the responsibility of the licensee to meet these requirements, even for personally owned radios.
Most of your requirements are not a challenge.
Water resistant is pretty easy to do. Most quality two way radios will have some level of water resistance.
Programmable in the VHF range isn't an issue
Scan mode isn't an issue, just be aware that scanning risks someone missing a call.
Where you'll run into challenges is with the "Chirp" software. Quality commercial quality radios won't use Chirp. Chirp was a piece of software written for amateur radio/hobby users. While it will support some low tier commercial radios, it's not something that will work with the sort of radios you probably want.
The FCC part 90 certification is something that is required under your license. It's not optional, and it's something that is often missed by those that do not understand commercial/public safety two way radio rules.
The Baofengs are not suitable radios. They are a cheap Chinese radio designed for hobby use and have no place in public safety. Many do not have the FCC Part 90 certification that is required under your license. I would not want my local fire department relying on a $14 Chinese radio when it comes to my life.
I know cost is always a challenge, but there's really good reasons that the quality radios cost more. If cost is really a concern, stick with the pagers. If you want reliable radios, then make sure your people get the right gear, especially if lives depend on it.
Kenwood, Icom and Motorola all make suitable radios that will do what you want. Kenwood and Icom have some entry level radios that will do what you need, as well as support two tone paging, so they could replace the current pagers. Easy to get those in the $200-$300 range, and they'll meet the FCC part 90 requirements. Programming software isn't free, but it's not expensive, either. It's designed for the radio and will work correctly and not risk borking up and screwing up the radio.
Another option to consider is to check around with larger local agencies and see if they are surplussing any used gear. I'd put a properly maintained used Kenwood/Icom/Motorola radio up against the Chinese crap radios any day.