I'm not sure looking at cost will help you make a good decision about stone selection.
The thing is, stones have sets of attributes.
In no particular order, here are a few and by no means all, and these are just my words for them. There isn't an industry standard that I am aware of.
Hardness - Soft like chalk, hard like granite, and a wide range in-between.
Feel - Silky, sandy, glassy, skatey, draggy etc.
Feedback - How well can you feel the edge angle on the stone through all the "Feel".
Cutting speed - Fast, slow and everything in-between.
Setup time - Is the stone a splash and go or does it need a soak. Do you need to flatten it between each use?
Muddiness - Some stones have no mud at all, some can be virtually mud baths, and there are endless variations in-between and the mud itself has its own attributes.
How is this related to cost you might say?
Any of these attributes and combinations of attributes can be had in both cheap and expensive stones.
There are cheap hard stones and cheap soft stones.
There are expensive stones that cut very slowly, and expensive stones that cut very fast.
There are cheap stones that are very muddy and cheap stones that are virtually mud free.
There are expensive stones that last a long time and other that wont last but a few months depending on how much you use them.
You might be tempted to think that expensive stones possess more positive attributed than negative. Is that even possible?
If you are a pro sharpener and time is money, you might really value cutting speed and want a seriously fast stone. So fast is good right?
Well, if you are a sharpener that does it for pleasure, you might like a slow stone. Imagine sex being over is 2 seconds. I guess some people might like it, but......
You can see right out of the gate, something as fundamental as cutting speed has no universal right or wrong.
You might be tempted to think a stone that lasts a long time is good?
Well, stones that last a long time tend to not release much mud and if you like to play in the mud, you have a problem. Again, no universal right or wrong.
What about feel?
Same problem. Who is to say if sandy is better than silky? Who is to say draggy is better than glassy?
As you can see, there is so much personal and situational preference that cost simply cant be used as an indicator of well, anything but cost.
In my mind, one needs to learn ones own sharpening preferences and then through research and trial and error, find a best match. Of course, this is all great fun, because as your skills improve and you learn new techniques, the attribute set that that was right for you a month ago will change
The end result is this. Just dive in. Get some stones. Sharpen a bunch. Develop your skills. Buy lots of stones.... and Mark will buy a new Ferrari.... his old one is looking a little ragged