As someone who is working exclusively in fountain pens, here is what I can tell you.
There is a lot of cheap crap out there. These are likely the $3-4 dollar nibs you mentioned and are the ones included with most pen kits. They are mostly made in China and a lot of them tend to have the "Iridium Point Germany" imprint. Don't be fooled, this imprint basically means the little ball of irridium may be from Germany, not that it is finely crafted German nib. I have heard that some of these nibs can be good with a little work but, for the little extra cost, you can get a Jowo or Bock that will be better.
The next step up are the steel nibs. The main players are Jowo, Bock, and, to a lesser extent, Schmidt. In the US, Jowo is distributed through Meisternibs and Bock is through Pen Realm. Both site also have the necessary taps to go with the nibs. Both Jowo and Bock are mainstays in the kitless pen world and both camps have their following. The main reason they are popular is because they are consistently good and, once you have a few nibs, you can swap freely amongst your collection.
From there, things escalate quickly. Bock makes a titanium nib which is the same size as the steel and is bouncier in use but is a much more malleable material so is easily sprung in the wrong hands. These tend to be in the $75+ range. Some people love them, others hate them.
The top of the market is the gold nibs. Gold nibs come in both 14k an 18k and I believe both Jowo and Bock are available in both. What's the difference you may ask? About 4k. Seriously, it is my understanding that the difference is more historical with certain countries having laws aroudn gold content that led to one or the other and that has persisted to this day. I have used both and you would be hard pressed to tell them apart. May people claim vintage 14k nibs are springier and have more flex to them but the modern ones are pretty much equivalent. The gold nibs are also going to be the most expensive, starting at over $125.
One other thing to think about is customer expectations. If you are targeting the higher end market, there is a price point after which people just expect a gold nib or, at the very least, will question its absence. I'm talking $400-500 so, if that's not where you are planning on selling, you don't have to worry about it.
I hope that helps.