I had two spare aluminum tanks that I decided to upgrade to the new valves and have re-certified. The company that did mine late last year is no longer in business, so I had to call around to find someone. There were three companies that do that in this town. I priced at all three: one wanted $35 (same as I paid last time I think), one wanted #25, the third said the part was $7.50, and five bucks for the labor and five bucks for the recertification.
What a deal! It definitely pays to shop around. My 80# tank is not required to have the new OPD valve. Usually it is not cost effective to repalce the valves in the steel tanks, but if you can get that good of a price it might bear looking at.