Free human based domain name appraisers?

Go to forums.digitalpoint.com. There's a message board where people will give you ideas as to what your domains are worth. It's not an official appraisal, but they're pretty good and giving ballpark figures.

Note: Unfortunately, most domains aren't worth as much as people think.

Knowledgeable people rarely do some work for free. You can use estibot. It basically use ML algorithms trained on historical data collected from auctions to estimate the domain price.

Edit: I forgot to add, that you can use some of the popular domain name forums. For example dnforum.com have Appraisal section.

Professional web developer here: most domains are worth next to nothing. The ones that are worth something:

• Are single, common words related to a very active sales market (baby.com, cars.com, etc)

...or...

• Have established histories, so there are old links and existing page rank lying around to give a sizable head start in building something new, or better yet, continuing the old (with the already-established community).

If neither of those describe your domain, it is worth $10 or less. (I'll bump to $25 if it is unusually cute and you find the just right buyer.)