Basing it on money is not a good guideline in any industry that basis most of it's product on marketing and exploiting urban myths.
You can assume for the purposes of the conversation that by "$150", I mean "the best speakers that can be obtained for $150". *Some* of the industry exists through marketing and other gimmicks, but exactly what proportion is up for debate. Again, engineer-geek style audiophiles like myself are generally not so easily manipulated.
I could build a 50 dollar speaker that will sound as good, if not better, the many 5000 dollar speaker.
 Even if I were to stipulate that you could build a competitive speaker for $50 in parts (and I don't believe you, for the record), the speaker is still worth way more than that since a person would be paying for your time, expertise, and potentially any shipping or payment processing that was required. Furthermore, there is a raw cost of materials that makes pretty standard thresholds in pricing tiers. For instance, in order to minimize resonance, you have to have sufficient enclosure rigidity. This requires raw materials that will be a not-insignificant proportion of cost of the speaker, and in some cases (for larger speakers) set you back more than $50 alone (for a large quantity of decent quality MDF).
no. They are what people ignorant of the actual engineering say. They are also used because they are an 'opinion'
Seriously, this is just stupid. Just because a word is imprecise doesn't mean that it is used by ignorant people. Sometimes a certain amount of imprecision is desirable and expedient for the purposes of conversation. For instance, I am a software engineer. In some cases, we will look at a piece of software and claim that it is "buggy", or that the code is "messy", or that performance is "scalable". These are all very imprecise terms, but they are useful for providing a quite overview of the situation. More detail can always be used later (like the exact number of unresolved bugs, or the performance benefit from doubling the number of CPU cores), but for a quick overview, the imprecise terms does quite nicely. Likewise, though a term like "muddy" is imprecise, it has a widely understood meaning (described in my previous post) that is helpful when communicating with audiophiles or especially with audio engineers.
Spoken like someone who doesn't like his statements to be testable.
Don't take my sentence out of context. In many cases, engineer audiophiles will provide graphs to show a variety of things, especially frequency response. However, textually describing such things is a huge pain in the ass. Let's say you're listening to some new speakers, and you notice a gigantic hump in the frequency response (5dB in amplitude) starting around 250Hz and ending around 400Hz. (just 50Hz past the bass-midrange crossover). According to you, why the fuck can't we just call it "muddy"?