I've been looking for a full sized foldie and stumbled across this model for $330:
Vilano Midtown 26 Inch Folding Commuter Bike, Shimano 24 Speed Disc Brakes
The online specs are sparse, but I called the company and it's 28lbs, uses Shimano 310 shifters and Altus deraileurs. I'm tempted and am deciding between it and a Joe C21.
My main concern is quality control.