New Approach Introduces New Difficulty

Realizing that the goal here is not to get really good at math, but to start actually thinking in a different currency, I tried comparing what I was buying to other purchases I had calculated in milliEther.
So, trying to guess the price in mE is even more difficulty when I have no idea what the product is worth. Today I purchased some cables (phone to phone patch and an XLR microphone cable). My best guess was that each cable was worth about Big Mac sandwich. So my initial guess was 12mE.
They were a little more expensive (about a 6 pack of brew each).
XLR and 1/4 phone patch

My Guess: 12mE
Actual: 16.23 mE