Jtag consoles are considered rare so whoever even sells one likes to penny pinch for the highest price.
I've got a jtagged zephyr board that I'd like to sell off, but it needs a reball and you'd have to rebuild the rest of the console around the board. (case, dvd drive etc) Thats about the best you'll get for $100 or less. My advice would be to try to save up some more money to buy a full jtagged 360 from elsewhere (not digiex)