Why do you think it's too costly? It's well known that there are divisions in DPRK that are focused on generating $ through crypto hacks and compromises.

We're dealing with reasonably sophisticated state actors here in this dark forest; not script kiddies.

Cheap $5 PCB + programmable small FPGA is a very viable route too for hardware implants; but even a microcontroller / ESP32/etc will probably do.