Cost for insulating an existing (bare) tank

[LaSalle1940]

Suppose there's a need to insulate an existing API storage tank in, say, a refinery in the northeastern United States. This tank is approximately 125 ft in diameter x 50 ft high, and we're talking about insulation to minimize steam consumption for freeze protection/maintenance of a minimum temperature. Is there a reasonable rule of thumb for the total installed cost of such insulation, based on thickness and the square footage to be covered (that is, for budget purposes, figure on $X/](square ft)(inch thickness)] )?

Thanks.