Did I miss something?

You can buy a GNS430 on eBay for $6000 and have it installed for $1000. I
did.

A King HSI will cost just about the same on eBay and to convert it to
Sandel will cost a minimun of $7000. You might get $1000 for the King HSI
indicator.

GNS430=$7000---used, installed
Sandel=$12000-----minimum, used equipment, PLUS installation


Karl