Sorry no idea in santiago.
BUT if u drive through Imbert there is a store that sells exclusivly cigarettes and liquor.......
my cigarettes in my village 1350 pesos a 10 pack, 1500 pesos sirena/national, in Imbert 1275 ( or 1250 ). So quite a diffrence for large quantaties.
I bought Gin ( saphire bombay ), vodka ( french grey goose or something ) and champagne ( tattinger rose ) for cheaper than sirens/national.
It is on ure left before the bridge (heading towards santiago ). There is a caribe express money changer next door, u cant miss it.