This is just an observation based on this topic.
Rack Extension developers, including Propellerhead, are free to determine the price of each of their REs, and I would imagine there are a multitude of different reasonings behind each pricing.
For example if we start at the bottom, some developers will chose to give away a RE for free. This might be for promotional purposes to create some sort of branding relationship with the RE market, or the simple will of wanting to contribute and give back to the user community.
Then you have your $9 REs. From what I've learned this is the lowest price you can set as a RE developer. As it currently stands, it seems like, what I would call, "the independant developer", has been releasing such REs. These devices, from the looks of it seem to be "utility" cv type REs. Some of which are straight and to the point, but never the less are all brilliantly designed. I personally like this type of RE, as it really plays into the modular aspect of Reason. These developers can be pretty heavy Reason users, and for that reason (no pun intended), you might see devices made out of necessity, which makes sense since these are typically cv utilities. I have yet to see an effect or instrument RE at this price point.
I would love to see more modular REs like dedicated vcos, vcfs, vcas, and adsr types. We already have pulsar which is absolutely fantastic as an lfo, and can also double as a wicked set of oscillators.
Then you have your $19-$49 range. This is where it starts to get more cloudy in terms of pricing and type of RE. So far we are seeing mostly studio fx, some creative fx, and a couple instruments (if you include pulsar as an instrument). I would imagine developers releasing REs in this range, have to start weighting the time and resources spent developing the device, functionality, what they predict the market will pay for such a device, and whether or not it's a straight "plugin" port or not. I've also noticed, in this range, we have smaller, but still well known software developers (with the exception of few).
Last but not least, we have the $50-$200 range. Most of these REs seem to be some sort of port over from a pre existing "pre priced plugin" with the exception of Props higher functionality REs, and one very awesome realtime sampling/granular/glitch RE, that I hold so close to my heart. In this range, if the RE is a port, the developer has to be reasonably competive with their pre existing plugin counter part (as long as it is an actual port). This is where I think you'll see most of the "big boy toys", such as synthesizers/romplers/samplers with "über" functionality, and really "out of the box" thinking creative fx. Basically, creative and useful sound generators and manipulators.
At the end of the day, I think the market will decide what stays and what goes, developers can chose to price their products how ever much they desire, but it's the user that will determine whether the developer continues to release REs. I personally can't see a developer continuing to release over priced REs that nobody buys, just due to the overhead and development costs involved. They will either stop releasing REs, as it just won't pay to release them, or they will lower their prices, to hopefully generate more sales.
So if you really like what a particular RE developer is releasing, and the price point is correct (for you), you should probably pick up that RE you've been eyeing in the propshop. Support the developers you like and encourage them to release more wonderful devices at said given price point. I also recommend using the try option in the store if you are unsure of a device's functionality, or if it is even right for you.