Seems absolutely reasonable. 

We never, ever, ever research without getting a written committment from the client via email as to the costs.  We provide a not-to-exceed cost estimate that bears a caveat allowing for additional costs upon written approval of the client.  Otherwise, we make sure to have a clear statement of understanding of the research cost which are explicitly accepted by the client before any work is done.  This is typically sufficient for us to have an established "meeting of the minds" as required under Contract Law. 

We were burned once early in our firm's lifetime, and we will not repeat that error again.

We'll incorporate the essence of this statement into our very, very  long list of discolsures, notices and disclaimers.  Thank you for it.