Thank you all for your insights. They are very helpful.
It looks like if I can get the appraisal reduced by at least 25% it would be financially worthwhile to get a private appraisal, particularly since the reduction in value (percentage) should logically carry over to future years.
Unfortunately, it also is clear such an appraisal would be complex and time consuming. Since the hearing will probably be within 30 days it is probably not realistic to expect to have the private appraisal done within that time frame. I am sure any attempt to do so would result in a higher, possibly much, fee, which is understandable. Possibly a better idea to plan for next year and take the time necessary to do it right.
This brings up the question of whether or not to even go to an appeal this year, with only the information I have been able to obtain, which may be insufficient. It might serve only to tip off the appraisal district with no tangible result. I know it is not within this group's purview, but would be interested in any comments as to the best strategy.
Thanks again.