The difference between a Moby and a woven is that a woven won't stretch so you can use it for a much heavier child. And you can use it for back carries which I awesome.
They come in different materials - cotton, linen, silk, wool, alpaca, etc and in all different blends as well which effects the price.
And some wraps are handwoven (Pamir for example) and fetch an amazingly high price as they are very limited.
Woven wraps all have different qualities and there's a huge difference in the comfort factor between makes, all which also effect pricing.
My most expensive wrap was $185 and I only paid that because I wanted the dinosaur pattern for DS.