"Which vaccinations?"
If you are in the USA you can spend thousands of dollars for all kinds of vaccinations before traveling to South America.Getting vaccinations can range from required for entry, to reasonable to completely absurd. If your vaccinations are costing more than your plane ticket you are probably well over the absurd range of things.
Are you going to tropical areas? Yellow fever areas? Remember, South America has a larger land mass than the United States. It varies from tropical, to cool (and cold) mountain regions, sub tropical areas and basically arctic areas.
If you visit, for example, Bogota, you will hardly get yellow fever, as Bogota is NOT tropical being in the mountains. However, you may need the yellow fever vaccination to enter other South American countries after having visited Colombia, even if you weren't in a tropical area of Colombia.