I think the worthwhile factors to consider might be: speed / effort , comfort, and reliability.
For OP, competitive performance does not seem to be yet another factor.
A lighter bike is generally faster - that takes money. But for 20K, the speed difference by lowering weight maybe 4 lbs likely would not justify the difference between 1,000 and 4,000.
To get a good fit, you often but not always need to spend more money.
Reliability. I put a lot here. Better, more ergonomic shifters = reliability. Simpler = more reliability - ie an old bike with downtube shifters will be more reliable in one sense, but take more intentional effort to shift, so are less reliable in a sense. Dinging a steel frame will not impact reliability of frame as much as carbon or aluminum. I think the hydraulics of disc brakes adds to problems as time goes by, so lower reliability. Very light spokes = spoke trouble = lower reliability.
Theft of a $400 bike versus a $4,000 bike: you can reliably go out and replace a $400 bike much easier.