Is it difficult to write a Linux device driver?

Question

Do it yourself

There is a Raspberry PI (or Orange Pi) with Raspbian.
There is a HopeRF RFM-95 LoRa module (connects via SPI interface to the pins on the Pi)
How difficult / expensive / time consuming is it to write a device driver so that the module can be accessed as a device (like echo "1234" > /dev/lora.rf95) ? How much does it cost to freelance?
There are ready-made libs for RF95 in C ++ on the github (but they are all designed for Arduino).

Answer 1

The official documentation though. As you can see, there is also an analogue of your example.