Check the Buell Service Manuals link at the top of this site. The service manual shows you exactly how to do it. It's really easy- my speed sensor died a few weeks ago & I had to swap mine out too. It took about 1/2 hour.
Also, before you buy a new one, take the old one out & make sure there arent' any metal chunks stuck to it. It's a magenet & metal chunks can get stuck to it & prevent it from being able to pick up properly.
The part was about 50, I forget exactly how much though.