Best bang for the buck


What’s been the most cost effective item you purchased for your system? 
I will go first- a Zerostat I bought 40 years ago. Next most cost effective purchase has to be a Denon DL103R cartridge which I bought new for $300. 

zavato

When we added a room to the house, and  had to add a sub panel. when I realized how close it was to the hifi, I said give me that 20 amp outlet. Took the guy just a few minutes.  I did add a better outlet later.  Total cost was maybe $200.

Dirac $299.  After that it would be the several thousand I spent building acoustic panels.

"Dirac $299.  After that it would be the several thousand I spent building acoustic panels."

Nothing left over for head reduction surgery?