I would concur with the general concencus that you can't beat a traditional wired comms system in most scenarios.
However would a Zoom/Teams/Webex/(Other video conferencing solution of your choice) meeting with video disabled achieve something close to the result you are looking for at the budget/free end of the market? I doubt that there are niche free/cheap solutions out there, that are more reliable or stable than the conferencing options?
There are plenty of POC apps, free and subscription that do PTT, (have a search for TASSTA or WAVE) - few offer "full duplex" though...
