Surprisingly, the 84 x 48 Nokia LCDs are actually cheaper than your typical 2-line text LCD, and they require fewer pins to control too. http://www.sparkfun.com/products/10168 The only downside is they all seem to have problems getting the contrast right, as it somehow varies depending on the temperature and force between the LCD and the circuit board. I have two of them, and they both change contrast if you push on the LCD frame with your finger. But for a $10 serial graphical LCD, I can overlook that.

I've got it using the Nokia LCD now instead of the color TFT, and everything is working pretty nicely for read-only emulation. I'm only able to go up to a 4 MHz data rate with the SD card, but I think that's due to my messy breadboard wiring. Viewed on the oscilloscope, the clock signal looks pretty bad, so I'm not surprised it doesn't work at higher speeds.

I'm going to start work now on a custom circuit board for this thing, which should hopefully improve the signal quality too and make faster data rates possible.