Digital Pot! THERE's an idea... There ARE "Digital Pot Chips"..
Anyone have experience with them?? Any that can handle 220volts??
Maybe several opto-triacs and resistors?? Like the MOC3061 (scroll down to it here: )
http://arduino-info.wikispaces.com/Popular-ICs
If the Solid State Dimmer Unit is $10 or so, the cost has to be pretty low...