Do craigslist finds count? If so...

Pioneer Laseractive w/ Mega-LD module + manuals for both + Laseractive branded controller + remote + a box of appx. a dozen games = $100 (steep, yes, but well worth it as the system was in beautiful shape and has worked great since I purchased it about a year ago).

Vectrex + 3D Imager = $100 (another steep one, but worth it for the Imager - came w/ the 3D Minestorm color wheel, and I had to spend another few months tracking down a reasonably priced copy of the cart).

Non-craigslist...

TurboGrafx 16 + CD-Rom + carrying case + loose copy of Air Zonk = $5.00 (yard sale find)

And one more for good measure ...

Chrono Trigger + Breath of Fire + Contra 3 + Romance of the 3 Kingdoms II = $3.00 each (SNES - thrift store find)