The Lead Appraiser will need time to meet with you to plan the appraisal, perform some preliminary evidence review (called "Readiness Review") and then to perform the appraisal.
They also charge for all travel expenses as well as time they spend away from your site to do their preparatory and concluding activities. Also, they will often work by the "book". Meaning, a guidebook exists that assists with planning appraisals. The guide suggests that, based on the scope of the appraisal, appraisals be scheduled for a certain duration and not be condensed into fewer days and longer hours. Lead Appraisers are free to charge whatever they want. not many charge the way SEI does.
Someone will also need to provide Appraisal Team Training to the people you plan to have on the Appraisal Team. This takes 2 days and is usually done by a Lead Appraiser, and best if done by the Lead Appraiser you plan to have doing your appraisal.