Tony,
I haven't priced any K2 machines myself, but yes I do think they are charging fair prices.
They're in business so they must be selling their products. If they're selling products, then they must be priced fairly.
I think it's possible to build a CNC for $4000, depending on what you want it to do, and what come on it. I mean, a good spindle can cost more than $4000 by itself, but if you keep things reasonable then 4K is doable. However, it would be crazy to ask someone else to invest their time, knowledge and capitol to build a machine and sell it for cost.
My neighbors build machines for the semi conductor industry. They build machines that pick up chips that are .005" x .010", and they pick them up with a vacuum tip and accurately place them on a card or tray. But I assure you, $4000 wouldn't come close to the cost of these machines.
In the end, what's important is what you do with it to make a profit. If you do that, then really the machine is free, right?