In the end, I decided that I don't want to throw any more effort at this damn thing, so I decided to spend a remarkably modest $230 (plus shipping) on the step-up Samsung CLP-620ND (21ppm color or black&white, duplex handling built-in). Street price seems to typically be twice that, but Amazon fronts for a variety of no-name resellers, including one called "eSeller" who seems to have positive reviews.

I figure, no matter the extent to which this vendor screws me, I'm really dealing with Amazon, so if it shows up DOA or something and the vendor gives me grief, I'll still have some measure of recourse.