A WAAS unit is worth $6,500 used in good condition in today's market. It costs $3,500 or so to upgrade non-W to W. The upgrade comes with a warranty and a basic overhaul. So, a new upgrade is worth more than $6,500 by a little, say $7,000 max. That would mean you need to get the non-W for $3,500 max if you want it to end up a -W unit. If not, then that's a great NAV-COM and IFR GPS for $4,000, but probably still a little too expensive.