Having 30 years experience repairing avionics from KX 170 systems to KY 197 and KX 155 systems, the problem is not always in the unit. Send an E-mail and we can figure out what to do next.
KX 170 systems run about $200, KY 196/197 systems about $250 and KX 155/165 about $350.
These are average prices for labor if the parts are available.
I work mostly with sport and experimental aircraft systems.
NOTE:: I am a component level repair technician. I will not change a circuit board unless it really needs to be changed.