I don't know of any "low cost" fully balanced amplifiers from input to output. Emotiva has some of the least expensive fully differential designs but most amps that claim "balanced" are nothing more than single ended with a phase splitter on the inputs. Please give an example of an inexpensive fully balanced design as I'd like to see it. thanks.
For power amps, it was only the Emotiva XPA-1 I had in mind at the time. ATI's least expensive model cost more but not by much. I know a lot of people would not consider those low cost and they would be right. I did a quick search, and found the TEAC AX-501 integrated amp also claimed fully balanced, but on a closer look, only the preamp section is fully balanced.
After posting I realized I should not have used the "low cost" term that is highly subjective to define. Put it this way, I am skeptical about any >200 WPC X2 and <$3,000 (list price) class AB end to end balanced amps but that's just me.
By the way, I seem to remember you have a very nice article on AH that describes the fully balanced input to output (all stages) configuration, with some sort of block diagrams or simplified schematics. I also remember the Denon pair was used as an example in that article. I wanted to link it but for some reason, could not find it via a key word search. Can you kindly provide a link please?
There are so much info on the internet but I always find those in the AH AV Research are the most informative and reliable ones, I suspect you may have some background in Quality control management, seriously..