I just got one of the $50 models a week or so ago. I read up a good amount on them, and they were reported to be one of the most consistent consumer scales available. Note that consistent isn't the same thing as accurate - especially on the BF numbers. I don't think you can really get an accurate BF measurement using those methods, but if it is at least a consistent measurement, you could track progress. The scale has been very, very consistent on mine (multiple readings at the same time within .2 lbs), but I've seen from 10.5%-11.5% from morning to morning on the BF comp. As a somewhat aside, I'd say I'm a bit less than that, but I haven't been measured in a while.
Note that many of the models (such as the one I got) only measure BF in .5% increments, which is a pretty large step and really makes it difficult to track progress. The variance I'm seeing may be due to real fluctuation that is compounded by rounding errors.
FYI, the only brick and mortar store in my area I found to carry them was Bed, Bath, and Beyond. They've always got 20% coupons going around (also accept coupons from Linens N' Things). Seemed to work out to a better deal with the coupon than even ordering online.