Production costs for the GDOOR bus adapter, incl. shipping and taxes, are ~ 40€ to 50€ for 5 adapters (Minimum Order Quantity). Additionally you need an ESP32 (~ 10€) (e.g. Buy here).
The GDOOR project is a non profit project by home automation enthusiasts. We do not directly sell the hardware adapter, but we tried to make it very easy to procure one yourself, fully assembled.
You have three possibilities:
You can order fully assembled hardware adapters from JLCPCB. You need to: