I gather those are fees charged by the bank for a loan, but I don’t understand why they’d be so dramatically different on a loan that is only $20k different. 

This is standard Fannie Mae guidelines, so this is not necessarily how HELOCS are calculated, but it wouldn't be dramatically different though. 

And sometimes with a city like Saint Louis the environment can change very dramatically based on minimal distance.

House hacking will be more advantageous for you, as when you rent one or more units, not only you get money that covers or go towards paying your mortgage payment, you also get to depreciate the % of the building that's rented, and your tax deductions increase dramatically.

It wouldn't be a dramatic difference either way. 

Depending on the extent of your project both areas of cost can vary dramatically.

Does insurance go up dramatically?

I'm right about 90% of the time, but the 10% of the time I'm wrong doesn't make me stupid, or unethical...I just lack experience.Another possible reason for overvaluing that I've personally encountered is the market shifted dramatically between when I bought the house and sold it.

Condo prices have slumped dramatically in many markets.4) There is an inventory glut of condos, which, again, will affect timeshares.Those are my bests guesses.

It might be easier for you to rent out the house altogether; Covid has changed how renters feel about living in "shared" spaces and the demand for SFH has dramatically increased.