CMOS-555 Theremin

My friend Wolfgang Dorninger asked me for a recommendation for a Theremin workshop. He wanted a cheap and beginner friendly DIY Theremin kit. He sent me 4 links and I should choose my favorite. After watching a Youtube video and listening to sound examples , I came to the conclusion that all of them were either not playable, ugly sounding, not DIY friendly or too expensive and decided to design my own Theremin with these specs :

about 10€ for PCB + components
PCB single sided with wide traces and large solder pads for DIY
non obsolete standard components
simple operation with only pitch antenna and no adjustable parts beside the pitch potentiometer
distance range of at least 50cm