to LAX OR MIA? No commercial airline that I know of flies from Valparaiso but several fly out of Santiago (100-150 km from Valparaiso) and ALTA (LA PRIMERA AEROLINEA REGIONAL DE CHILE) flies small planes out of VIŅA DEL MAR which is very close to Valparaiso (but not to Santiago directly?). I would think your best bet is ground transport.
On Lan Chile
SCL-MIA - 2 flights daily, one leaving mid to late morning the other around 11 PM.
SCL-LAX on LA0600 23:10 07:40+1 DAILY