The XIM3 is $150.
The XIM2 was $180 and required a computer. The XIM3 is its own device, it is supposed to more responsive out of the box then you could get the XIM2 to be, mostly because the timings on USB aren't being handled by another system. The input lag on it is the same as that of the controllers, 8ms. I plan to get one so that I can play with my sisters in Halo without having to deal with joysticks for aiming.
I think you can use almost any device with it if it uses standard HID stack, but thats when firmware gets perfected. Stuff is still getting checked for compatibility, I don't think any fightsticks are there yet.
Compatibility list