I am attempting to contact person[s] in an organization responsible for doing all legwork in getting health insurance bids, dealing with the renewal process, etc., for businesses 50-250 employees.

Any thoughts on titles, mailing lists, etc.?

Thanks.

Michael:
My experience has been that in companies in the size class of 50 to 250 employees the controller or some other finacial person is usually in charge of the benefits. They may not make the final descisions, but I would start by contacting them.
Are you attempting to sell something?