Is PR a commodity?

The other day I saw an electronic marketplace that matched common folks beset by legal problems with lawyers willing to auction off their services. A person who wanted a divorce could use the marketplace to find the cheapest lawyer. Thanks to the marketplace lawyer's services became a commodity, assuming, of course, that all of the lawyers were more or less equally competent.

I confess, if I were on trial for murder, I'd seek out the best lawyer I could afford, not the cheapest, but for wills and uncontested divorces why not go with the cheapest competent provider?

Could there be an electronic PR maketplace? Do we all provide the same basic skills? Is it all about measurement? How can you tell one firm from the next using only a generic RFP and an hour interview? Picking PR firms this way seems like an awful combination of Match.com and speed dating, a system that has some successes but mostly ends in failure.

Am I wrong in this? Is PR like murder trials or more like basic wills?