It's not appropriate to talk specific prices per forum rules. But this one is easy I think. You could just word it that the one guy is charging X and the other 4X.

From what you described, the guy charging X was going to do a heat load calc. That's nothing but paperwork that estimates how much air you need for each room. It sounds like you're saying that the second guy will actually fix some ducts and get the air balanced for 4X. Is that right? If so then the quotes are for very different services and the price difference is very understandable.