I have the cateye strada wireless, picked it up on amazon for about $50. Easy to install, works great. I like the clickable screen which is easier to use than buttons. I personally wouldn't put it on a mountain bike - it doesn't have the feel of high durability...not to say it is flimsy, but it is all plastic.

For the basic functions, I would probably go with a cheaper option. Many models are around $25-50 making them somewhat disposable in case of a crash.