My father is an attorney and I'm an engineer. He would tell me about how much money these expert witnesses are making per hour and would encourage me to look into branching off into it. The way I see it experts are expected to be ready to get up, say what's going on, and charge by the hour. As far as experts go, i personally think there is more measurable professional accuracy demanded of engineers than doctors, psychologists, law enforcement, and lawyers when it comes to what is said in court. I think this translates to more time spent in preparation (or it should) than is justified, since they're all experts. Many experts get to spout out conventional wisdom and anecdotal evidence for there field and walk away.