Isolation transformer? I might go along with that for the control circuit for the motor controls, but that's it.
If nothing else, he simply doesn't have the power available.
True, we're not on-site, and cannot know all the details. Yet, as my earlier post suggests, I've seen this scenario all too many times. I suspect that many borderline compromises were necessary for the OP to get painted into this corner - and there's a world of difference between 'code compliant' and 'good design.' Those poor choices have finally caught up, and are no longer adequate.
If he does anything - panel, transformer, whatever - to make the location have more than one circuit, he has a separate structure that requires a 4-wire feed. Especially with the revisions in the 2008 NEC, that's what he needs. He also needs a ground rod.
Off on a tangent ..... one of my 'wish list' items is a nice, little, very quite generator. Just enough for a tool and a light. Premium models sell for about $800. If this guy's needs are truly that little, such a generator will solve his problem, and for a lot less than installing a transformer, replacing his feed, etc.
