I would probably approach this from a different direction. Quality, like beauty, is in the eye of the beholder. Instead of trying to attach value to quality, I would start with..."How much should a bassist expect to pay for a performance-worthy bass?" By that I mean a bass that you would be willing to use in a live performance setting.
After you establish that level, all other options or modifications would need to sort of earn their way in. Even then, we have to realize that some of the optional content lends N-O-T-H-I-N-G to the quality of the sound. That is why I propose setting the baseline at least amount of money to spend on a performance ready instrument.
Now, for a Fender Jazz / Precision type of bass, I would set that number at around $450. You can get a decent used passive Fender MIM for that price. You can get an SX for less, but in my limited experience with SX (donated one to a school, one to a church) I would want to upgrade them before I played them in front of a large crowd. I do occasionally play the 5 string I donated to a church when I play at that church. It'll pass, but the tone quality is in my opinion nowhere near that of any of my own 5 string basses.
For a more modern type of bass, I'd probably set the number a little higher, maybe $550, because you are almost always dealing with an active instrument, so you have a preamp included in the material cost.
Now, back to the quality thing. This is something that we deal with in my company. How does the customer define quality?
There's FUNCTIONAL quality / reliability. How well does the product do what it is supposed to do and how reliably does it do that? For a bass that is how good and solid is the tone? How powerful is it? Do you have to crank it to 11 just to be heard over the organ? Does it distort at high volume?
There's CONTENT quality. Bling. Goodies that don't necessarily translate into function. Cool pickguards and pickup covers and bridge covers. Gold plated or black tuners and bridge instead of the standard stainless. Mahogany core instead of basswood. Of course the wood CAN (but doesn't always) impact the sound (functional) quality.
There's PERCEPTUAL quality. This includes workmanship, both visual (pretty grains, precise contours, unique body design, well filed frets) and tactical (feel and speed of the neck, joint alignment, balance).
Different people attach different levels of importance to each of these areas of quality. And that is part of the reason we have so many choices as bassists. Different products excel in different areas of quality. The more expensive brands like Alembic, Ken Smith, MTD, Roscoe, Lakland, Sadowsky, excel in pretty much all areas and charge for it. For those who don't VALUE top quality in all those areas, these brands are over-priced. For others, the ability to get exactly what you want with top notch quality is an affordable luxury.
Peace,
James