As for the gear, there is NO MONEY in TV's at all. Sony used to mark up 21% and my overhead was 23%, so I lost money on every Sony I sold. I had to make it up on delivery and installation charges, unfortunately. If you loaded it in your car yourself, money went out my door.
As for the rest of the gear, I have no idea but people on here who sell or have sold that stuff have posted some info. I like the idea of asking if he would do it for 15K and see where it goes. He knows how much he is making and will do what he can to save the sale, I would guess, since you are a good customer of long standing. OR he might offer you a "free" service agreement of some sort to ensure your complicated system is working to its maximum capability. I would be surprised if you did not have at least 2 visits in the next few months to make adjustments. That truck still costs 125 every time it rolls whether you are paying or not, so that MIGHT be a better deal than a huge discount up front. As I tell most people, when you buy a car, you are buying the warranty, nothing more. Same here in some respects.
Ask--all he can do is counter at a higher number or say no. Either way, you MUST have a agreement for support for the next few months or so.
Cheers, and enjoy the music!!