By "truly great", what, precisely, do you have in mind? The ability to drive very low impedances? Very high power? Something that appeals to those who believe in magic in their equipment?
In general, it does not make more sense to buy mono power amps instead of amplifiers with more channels, as it usually costs more for the same level of quality to have all of one's amplifiers in separate boxes. This is due to a couple of factors, one being the economics of scale (basically, the more of a particular amplifier coming off of an assembly line, the cheaper it is per amplifier, as the amount of cost of each amplifier for setting up the assembly line is less due to the setup cost being dividing among them all, plus of course the purchase of the parts to make them [resisters, diodes, whatever] is cheaper per item when done in high bulk). And more power amps are made with 2 channels than there are mono power amps, so this means that you won't have to pay as much for equivalent 2 channel power amps. Another reason is that with mono power amps, one is paying for a box for each channel, instead of one box for more than one channel. The same idea applies to other things, like the power cord, etc. In other words, it takes more resources to make a pair of mono power amplifiers than a 2 channel power amp of the exact same level of quality, and those extra resources are going to add to the cost of the unit.
Additionally, having your equipment in more boxes means that it takes up more space in your home, and for most people, having 7 boxes just for power amplifiers would not be desirable.
Now, if you have money to burn, and consequently a house large enough to accommodate whatever you want to buy to put in it, none of these considerations will matter to you. But it is likely putting extra money into the equipment without getting an actual benefit in the sound quality.
My best power amp (in my opinion; people who believe in magical equipment would pick a different amplifier of mine that is a design that appeals to such people) is a
Crown K2, which, unfortunately, is not made anymore. I use it to drive a pair of
Apogee Stage speakers. It is more powerful than I need, and it is good with low impedances. If they were still made, I would suggest getting one of them at the price point you are considering.
Getting back to your question as asked, if I were looking for mono amplifiers in your price range, I would seriously consider:
Emotiva Audio XPA-1 Differential Referenceâ„¢ Mono-block Power Amplifier
You can read a review of a lesser 2 channel amplifier from them at this site:
Emotiva XPA-2 Two Channel Amplifier Review — Reviews and News from Audioholics
However, the manufacturer does not recommend them for 2 ohm loads, so whether you would want to consider them or not depends on the speakers you are planning to use with them. For seriously low impedances at your price point, you probably want to be looking at professional amplifiers, particularly if you want a lot of power.
