Well, I have a classic Mac, and I don't have ADT Pro.
It's not possible to do Appletalk on the IIc+, which is why you're coming up empty. And depending on what other hardware you already have... ADTPro is free as in beer as well as in liberty.
What would be the costs associated with my getting ADT Pro and associated equipment, vice using what I already have
You would need a null modem cable if you don't already have one, and you'd need a USB-serial adapter if you don't already have one.
and what would be the gain to make it worth my while?
Uh... you could communicate to the IIc+, whereas now you cannot? ;-)
