Just a warning on buying trays from some avionic vendors:
Several years ago, I bought a tray from Stark. When it came time to buy the transponder, I decided to go with another vendor. This is where I found out that I was overcharged for the tray (the backplate was not provided as well).
When I spoke to Stark about this, he said they charge higher for the trays, and discount their avionics when you buy the rest of the package. I did not agree with that philosophy (wish I knew in advance). This solidified my decision to buy from the alternate avionics vendor (taking a small monetary loss at this point).
Stark may be a good place to buy avionics, and his support may be at par or better than the rest, however I also value other aspects of a business transaction.
My 2 cents.
Alfio