I have no idea what it costs to get a used radio, or what trays are interchangeable. Is the whole panel non vendor specific (I find that hard to believe)? Obviously a Michel won't fit where one of those old analog radio dial ones is...
Yes, the whole avionics stack is NOT vender specific. Most light aircraft from the early 60's and up have "standardized" rack mounting systems similar to the way almost any vender's hard or disk drive will fit your PC computer. The avionics shops just change the tray to match the desired brand, make the connections, and slide in the new radio. Find a good radio from a Piper or Beech, etc., and install it in a Cessna.... no problem! Michel is a MAJOR supplier of replacement radios for Cessna ARC 300 and 400 series radios, because in most cases you don't even have to change the tray! Most Michels use the original Cessna ARC tray, or they supply an adapter or tray with their new radios! The Michel MX-300 digital flip-flop is a
direct slide-in replacement for Cessna ARC 300 series analog dial (that's one good reason why you see so many Michels in Cessnas, not to mention Michel's support)!
Bendix-King makes great radios, but their systems are too often proprietary (no brand mixing - so you often have to use BK components if you add-on capabilities later, such as ILS or DME, etc.). They are also more expensive than nearly all other brands, so I would avoid B-K avionics unless you already plan to swap them out. Otherwise, most brands are compatible with most other brands, with this one big exception and possibly one or two more smaller exceptions.
