Crossfit has gotten tremendously popular and thus a lot of people (personal trainers) are trying to cash in on it.
I don't think most people need a personal trainer. In terms of crossfit the only thing I'd pay for is some instruction in how to do the olympic lifts using a barbell (and I'd probably be happier to join a weightlifting team/coach to learn this than someone who got a crossfit certification). However, I'd probably just skip those WODs (since they appear to be chosen at random anyway) and use the KB lifts instead.
Creating a crossfit home gym can cost you anything from a very little to a few thousand for olympic standard weights and platforms. This is where I like the KB. It costs much less and takes up far less space.