It's true the same thing can be fabricated cheaper, which is what I do here, but for $35 the DINAH is actually a good deal. A big plus with the DINAH is that the onboard GPIO pin on the CM108/119 chip

UZ7HO's SoundModem recently added FX.25 also.

With the Fe-Pi you have now, DIrewolf should be able to activate PTT from your choice of a GPIO pin off the 40-pin RPi header. Simplest way is using one 2N2222 (or equivalent) transistor and one resis

Not sure if this is along the lines of what you want, but here's a basic walkthrough for installing Direwolf and linBPQ on Raspian Stretch: https://www.qsl.net/swlkp3/DWbpq.rtf