Greetings Chad:
Practically all hardwood species, including black walnut, have taken a serious hit in light of the economy. I wouldn't be surprised if you indeed have some veneer quality walnut trees, but of course I can't determine that without physically seeing the trees.
Some consultants don't charge a fee for an initial visit, whereas some will charge a fee for an initial visit - there are no standards or set fee structures to provide you.
My suggestion is to contact a local consulting forester and ask them what they would charge, if anything, to evaluate the marketability of your timber. I can also most guarantee that most consultants will tell you to hold on to standing timber until the hardwood market rebounds. However, the consulting forester will be able to tell you if you have something valuable or if you have something that is simply marginal.