in my experience, Paint Shop Pro goes for under $100 (not altogether sure about that tho, may have been a sale), and I think X2 is the latest version (in other words, v11.0, I think).
Since I started with Photoshop 7, I learned that and stuck with it, so I don't know the other programs very well. I can work my way around them though, so, there's evidence that they are fairly easy to use in comparison. As for feature differences, those I don't know anything about.
What makes them different to me is mainly the interfaces. They all do pretty much the same basic set of operations, and to my knowledge, that's all you really need for texture design. As long as you can paint and use layers, then you should be able to do everything you need. Some people like taking shortcuts though, by using effects filters and whatnot to achieve results. I don't particularly think you need them in order to get the job done, but they can help, and they aren't the same or sometimes even included in some software packages. Keep in mind though, that as long as you are using a very recent version of a software package, they've prolly included functionality capable of reproducing the effects in older versions of photoshop (part of that whole market share thing).
The alternatives I gave you are good examples of that and should suit your needs for a lower price. I'll stick with photoshop though, cuz I loves it. <3