I admit the Algo will probably cost beween $200 and $300.
If you have some electronics knowledge, you might be able to cobble together something to provide audio or tactile indication of the MWI current on an analog line. Another place to check for this type of stuff is
www.sandman.com (noticed that he also sells the Auxbox, catalog page 109).
Good luck and keep us apprised if you find a workable solution; we may be in the same situation someday.