Hi Mike:
Unfortunately, it is difficult to determine if your black walnut tree has any lumber potential without photos.
And to be fair, most certified arborists / tree service companies are not in the business of paying homeowners for useable portions of removed trees. This doesn't mean that a portion of your yard tree isn't suitable for milling into lumber, it just means that many arborists simply do not incorporate "log/lumber value" into their tree removal quotes. Again, arborists are in the tree care and tree removal business -- most are not in the business of buying or bartering yard trees for future milling purposes.
Something to also consider is asking the arborist/tree service company to simply retain as much of the main stem/bole for you to possibly sell yourself after the removal operation is completed. There are urban wood networks/directories in Wisconsin that cater to these urban wood utilization efforts.