Appraisers need to be certified. I would start with contacting the organizations that do the certification to find an appraiser in your area. Here is a link to AQS
http://www.americanquilter.com/about_aqs/appraisers.php
There is also the Professional Association of Appraisers
http://www.quiltappraisers.org/
Edited to add, I believe they need to see the quilt in person. Most have a questionnaire to fill out as provenance will make a difference in the appraisal, things like have you ever sold a quilt or won a ribbon at a quilt show or fair. I just had one done at a national show and it was $55. She gave me a very nice write up on the quilt with the appraisal.