???What's The LEAST Expensive "End Game"Amplifier You've Ever Heard???

I could live with my Firswatt F6 for the rest of my days, same would apply to my Dynakit st-35. Both are very pleasant with appropriate speakers and room set-up.

Simaudio 700i V1 or 2

Coda CSib

Krell 300i (surprised this one hasn’t shown up yet)

The D’Agostino Progression too, but not exactly cheap

Depending on your speakers a true end game amplifier that you wouldn't want or need to ever upgrade is the SE84UFO25 by Decware.  Two of the most musical watts out there.  The Decware owner actually made the first amp for himself as a state of the art  SET amplifier.  It turned out so good that he offered at over three times the cost of the SE84UFO and now the Decware backlog is an over three year wait time. 

It's a niche product for people with speakers in the 100DB sensitivity range but is truly a piece of equipment that you can inexpensively tube roll and tune for the specific sound characteristic  you desire.

I agree with you @danager! Those willing to DIY can bypass the waiting list and build their own with a printed circuit board and instructions from Steve Deckert for only $45.

https://www.decware.com/newsite/SE84CDIY.htm

the whole project cost me a bit under $600 a few years ago.

While I have bought a used set of PS Audio, BHK300’s and their Signature preamp, I still have a Hegel, H390 integrated and if bought used is one heck of a deal!