Instead of 4809 or 328P why not step into the 21st century and use a ATmega32U4?

[platima]

4809 - US$4.0, limited stock, req UPDI. 328P - US$2.2, plenty of stock, still req UPDI 32U4 - US$4.6, BUT, includes USB connectivity

Should be compatible - same 16MHz clock, plenty of pins, alreayd used by the Micro, LilyPad, etc.

Could pair well with a USB-C port.