You can say "X is three times the price of Y" - but that's not what this sentence says. This sentence says "X is being sold for three times the price (?) the drug's maker charges for Y."

C (that) is best here. You'd say "the same price as" or "three times more than" or "three times the price that." Given what's not part of the underline, we have to go with the last option.

I'm curious about the source of this question. This is pure idiom and it's not often that the official test makes us rely solely on an idiom (it does happen, but not often).

I am seriously unconvinced. What's the source?

By the way, I just did a quick Google search and found three different sites discussing this problem - one of which said the answer was A, one of which said it was C, and one of which said it was D.

So toss this one.