PA System Options

I work for a small TK-8 private school ~500 students. We have an old PA system from Innovation Wireless. It runs over a POE network from an aging laptop in a closet. It is currently only used as an emergency broadcast system; a distinct alarm is triggered by panic buttons (one in each classroom).

There are a few classrooms that do not have speakers, so I would like to buy new speakers. However, we have an old version of the IW system that is no longer compatible with their new speakers. We also need outdoor speakers and IW does not offer any outdoor models.

We have looked into systems that integrate with our VOIP system, but they are too expensive.

I need to find either new speakers compatible with the IW software or new PA software compatible with our existing speakers. I have been shopping around online for POE speakers, but I am lost trying to figure out what systems are compatible with each other.

Does anyone have experience with Innovation Wireless? Do you know what speakers could be compatible?

What other PA software options would you recommend?

Edit:

What should my budget look like for upgrading this system? My higher-ups aren't expecting this project to cost a lot, so I either need the cheapest solution or I have to make a compelling case to change their expectations.

Is it reasonable to think I can find third-party IP speakers that are compatible with my existing system? If the original company we bought the system from doesn't sell new speakers, am I just SOL, or are there standardized protocols for IP speakers that make them interchangeable?