selling used servers in bulk

You should walk away from this offer right away! They are asking top $ for old severs. Any server more than about 3 years old is a tough sell. No big business will buy those servers, and any small business who might be interested would only want one or a few. As olddude posted, scrap values for servers are all over the place, depending on make, model, options, etc. Sounds like they won't let these go for scrap value.
What you can do is check back with them in a few months.