From my standpoint I'd say $106 US is lot in terms of what the parts cost. However they probably have a custom programmed micro doing both the pwm and pi control of the temperature. And that probably cost them quite a lot, especially if they sourced it out. So they are just charging for the R&D. Then 106 dollars is perfectly reasonable to anyone who can't do that sort of thing for themselves.
Since87 is right about the switching, I could only imagine all the horrible harmonics that pwm might produce, but a simple second order low pass filter (inductor and capacitor) should be able to take out most of the harmonics and leave the dc component behind so you have nice more or less clean output.
Personally I would like to try this out myself and don't think it should be too hard. The pwm is easy to program in a micro, but the PI control, that will be a little harder since I've never done it. But one of my textbooks outlines a few procedures in implementing PI and even PID control in a micro. So once I have a chance I'm going to start.
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