Porcelain cabinet models were a $10 option with Sears in the 1960s, which John already mentioned. I have no idea how Whirlpool priced it, but I would expect it was in the same ball-park. There are great in moist enviroments like northeastern basements --- no rusty cabinets. You got a better deal when buying a model that wasn't full porcelain on the top and lid in the regular model, as it would have both these in the porcelain cabinet version for no extra money.
Sears seemed to spec the painted parts much more liberally than WP did in the 1970s and early 80s, though I never really understood the need to have a porcelain lid but a painted top. Eventually on these the lid looked nearly new in a rusted lid well (dumb).
When the powder coated tops and lids debuted in early 1983, this made a big improvement in durability over the painted tops, and suddenly many of WP's models were getting them along with most Kenmores under the 80 series. The powder coating is a much more environmentally friendly process, as porcelanizing requires chemical etchers (Hydrochloric Acid) and uses a lot of heat (therefore energy) as well. Not only is it cheaper and more environmental, powder coating can be applied more quickly.
Long term now that these first models are 25-30 years old, the powder coating seems to last much longer than the painted parts, without significant rust exposure, but they seem to get dull and scratched just like the painted parts.
Gordon[this post was last edited: 2/7/2013-16:11]