Whomever you let do it, do it all. I've been stranded by a valve cover gasket leak that ended an alternator, and let me tell you it's no fun. From my short experience, no auto parts stores carry LR parts in stock. If the alternator looks caked with oil/grime, replace it too.
Also make sure the vcg quote wasn't separate from the crossover pipe. I don't see why it would be that high unless they were quoting from scratch. The vcg is like $13 by itself and the labor to remove the vcg and some fuel lines doesn't add up to that price imo. The full price is about what my bill was for the vcg job at the dealer, but my warranty covered it.