I tend to think it works this way in concerns to the "fi"-ness of audio equipment.
Low-fi is considered what you find in every big box store that's price usually falls under about $500.
Mid-fi can sometimes be found in big box stores but is usually found in specialized audio shops and its price range is usually from about $500 to around $5000.
Hi-fi is only found in really, really freaking expensive audio stores and the price range, well, makes your jaw drop.
Of course, these price examples refer to processor/amplifier prices and not such things as headphones, speakers and the like. Also, internet only retailers can blow this classification completely out of the water. Finally, this is just my feelings about the terms and not really based on any particular technical info.

Of course, if you like the way it sounds and you can afford it, screw the classification and just buy it!! It all comes down to wether your ears like it and how much joy the equipment provides for you.