Yea for sure accels can be a hands-off prospect, and can be placed almost anywhere. I highly recommend them; they are very useful for all kinds of things. Just not something like Traction Control. At least, not cost effective.
Sorry Z, I can't quote exact numbers. I work with this stuff all the time, and although I wouldn't ever say for sure (technology moves pretty quick), it wasn't long ago I was involved in a project to do just this sort of thing. You can get wheelspeed type sensors for a couple bucks, double that for something really good. A real reliable accel that is robust and samples fast enough that you can filter it's signal to something usable and still reacts well will cost you over $100, maybe double that.
With a wheelspeed, dust dirt, hell it can even operate underwater, doesn't matter. They are awesome little buggers. And all you need are two teeth of rotation, and you've got a basically instant speed to look at.
Don't let me totally discourage anyone, like I said technology moves fast and this is the place where you have the opportunity to test out new things... but keep all the pros and cons in mind, and hopefully I've helped show some.