There is a lot of difference between a $300 and a $2000 bass. You're not paying extra for NOTHING. You are getting higher quality WOOD, FINISH, HARDWARE, ELECTRONICS and sometimes construction.
The key is whether you appreciate (or notice) the difference or not. Some people don't and if it sounds good and looks good
to them, that's all they need. And they're
not wrong.
I have a $2500 Spector Euro. I've played Spector's lower cost Legend (around $800 at the time) and there is absolutely nothing wrong with the Legend; it's a pretty good bass. But the Euro has a lovely quilted maple top with an impeccable gloss finish, better pickups (US Bartolinis), higher quality tuners (more on that in a sec), and overall it just "feels" like a higher quality instrument. Some may not care about this difference.
Car analogies have been used before so here's a new one. Anyone here play video games? Play a game on an Xbox One and it will play just fine. You're not really missing anything. Now play that same game on an Xbox One X. Now you have higher resolution (up to 4K), more consistent or higher frame rates, and in many cases, faster loading times (faster yet if you switch to an SSD instead of an HD). You can play just fine on the standard Xbox One. You'll still get a great experience. The Xbox One X gives you a little more.
And at the higher end of basses and above (especially above), you're paying for more hands on craftsmanship, finishing and attention to detail along with extra bells and whistles (fancier woods, inlay work and materials, unique finishes). Hours of human labor as opposed to an automated assembly line cranking hundreds of bodies and necks.
Finishes on cheaper instruments may also wear or chip more easily because they're not getting as many layers sprayed on and the proper amount of days in between needed to properly dry and buff (time is money).
That $5 tuner is not going to hold tuning as long as a more expensive one. I had a guitar with crappy tuners and after a few songs with heavy bending or strumming, one or more of the strings would go slightly out of tune. The usually higher gear ratio in a more expensive tuner will help you to tune faster with more accuracy.
(That $5 tuner is the Xbox One's HD, that $50 tuner is an SSD
)
Now, I'm not saying I don't like inexpensive instruments. Some are truly excellent buys and play and look great. And I agree that at some point you're getting to diminishing returns (as much as I want a U.S. made Spector, no way I will pay $3800 to $6000 (and higher) for a new one!).
I'm just saying that there IS a difference between expensive and inexpensive basses. At the end of the day though, there are many variables and if it plays and sounds great, that's all that matters.