A tip from Michael J. Wagner: When selecting an expert, don't automatically choose the expert with the lowest rate.
It there is a substantial reason for the higher rate, then the more expensive expert may be more efficient. Many experienced experts have higher rates because they have done the work before and can now do it faster . . . The result of somewhat higher rates and much greater efficiency may be a lower bill.
Source: "Expert problems," by Michael J. Wagner, The Litigation Manual: Pretrial (ABA Litigation).