Costs approximately $129.00 . This allows one person to use the software on multiple computers, or multiple people to use it on one shared computer.
To use (the popular Modbus master simulator) beyond its trial period, you must purchase a legitimate registration key directly from the official developer, ModbusTools . How to Get a Registration Key registration key modbus poll 2021
You might be tempted by a Reddit post or a YouTube comment promising a working key. Here is what actually happens: Costs approximately $129