So which is right:
there is an entire gamut of hidden costs associated with it OR
there are an entire gamut of hidden costs associated with it
So which is right:
there is an entire gamut of hidden costs associated with it OR
there are an entire gamut of hidden costs associated with it
The first is correct, because the number of the verb must agree with the number of the actual subject of the sentence, which is gamut, whereas hidden costs is part of a prepositional phrase modifying gamut.
gamutis a terrible choice of words here. It means a musical scale. To run the gamut means to play an entire one-octave scale, metaphorically to try all the possibilities in a sensible order. "A gamut of costs" is nonsense. – Michael Lorton May 08 '16 at 16:25