Domain appraisal is very subjective.

I'd say it's worth looking at namepros.com and dnforum.com where you might be able to get some friendly appraisals. Also have a look around for recent sales history. Try to find similar names that have sold in the past.

I wouldn't recommend paying for a domain appraisal. They're generally scams but usually way off the mark.

If it is a true generic domain like cereal.com or breakfast.com, then it's worth a small fortune. Like $500,000 minimum!

Have a look at: http://dnjournal.com/ytd-sales-charts.htm for the year to date big domain sales.

Also: http://www.ricksblog.com/ Rick Schwartz has made some huge private sales in the past, and he might be able to offer you some guidance.

Good luck!