Your price is high, period. I don't think any standard replacement (as you described, with a little ductwork) should run more than $12k for that level of equipment. You could replace 2 systems for that cost (though perhaps not with the level of equipment you're looking at, which is rather high-end). I think you'd do yourself well to have another estimate or two. Ballpark in one area may not be ballpark in another. That system should qualify for the $1500 tax credit and possibly other rebates you'd want to look into. Sounds like a pretty straight-forward installation with a little ductwork. A note on the return air grille: you really want more than 1 for a 4-ton system.

Does seem very salty but only way to know is get a quote on a comparable system from another dealer.