DIY keylogger

I was looking for keyloggers online(don’t worry it’s not for bad purposes) and saw 1 thing in common, they are All horrendously expensive for what they are. I was thinking of making my own. I know how to program this, but I need guidance on the hardware. I know what board I want, it is an adafruit feather 32u4 adalogger. I cannot find any good USB host adapter from some serial interface that arduino supports. Any tips?

Most host shields use the SPI pins. That will still work fine. You are connecting the keylogger between keyboard and computer, correct?