We paid a lot of money to get our yellow fever shots but there's no need. You can get them free here - "Dirección Nacional de Fronteras"(Border Health, the Ministry of Health), located in Calle Ingeniero Huergo 690 (corner Chile).
http://www.msal.gov.ar/index.php/component/content/article/48/272-vacuna-fiebre-amarilla
http://www.msal.gov.ar/index.php/component/content/article/48/272-vacuna-fiebre-amarilla