And there always is the clicking of the cadence sensor hitting the magnet with each pedal stroke.

If you don't find any problems with the components of the bike, it might just be the frame. A crack in the down tube or seat tube could be making the sound. If there is a crack, it would be a few millimeters from the BB shell, and it would parallel the weld between the tube and the BB shell. On your Surly it would show up as a crack in the paint, so that's actually what you're looking for.

If you haven't yet figured this out, the cause of my noise on my LHT was one of the chain rings. It needed tightening. I chased that noise for about a year, including a tour across Indiana and Ohio. I changed out pedals, checked the cassette and made sure it was torqued properly, etc. I finally snugged up the chain rings and that was it.

I have been riding for more than 60 years and my bike(s) have only seen the inside of a bike shop a handful of times.
Park Tool web site is wonderful for any level of mechanical competence to learn a fix-it skills. Don't be ashamed to watch a video (and there are lots) multiple times until you understand the process. Sometimes just an adjustment, sometimes replacement. Rarely can a problem not be diagnosed and solved. Your limitation is likely to be: do you have the tools for repairs. Your budget might be more strained with buying tools rather than getting something fixed.
Also, if the axle seems to have movement that you can elicit by just pulling and pushing the crank arms, you might not have to pay for parts, just the labor (which, admittedly, can be exorbitant). Ask this "mom's bike shop" what they charge for a bottom bracket maintenance. Might not be so bad...
Suggested reading: https://www.parktool.com/en-us/blog/...bottom+bracket