Re: Can someone give me an idea of what sort of money is involved?
I'm not sure it's even worth trying for full Exchange support these days.
Most companies that still have their own in-house Exchange server will probably have plenty of licenses for Outlook, if they don't, Outlook Web Access has pretty much all of the same features now, and finally Microsoft are pushing all their customers towards paying them (MS) to host Exchange.
On top of that, I wouldn't be surprised if more customers are dropping Exchange completely now (if having Microsoft host your email is an option on the table, why not move to Gmail or some other webmail provider?).