what if i rely on subway sandwiches only? 
i won't be buying souvenirs, i'm not that kind of tourist.
i wanna just hang around, walk around but not be a tourist and
go for attractions
like chill out, have a coffee... reading the papers, walk around
the shops (i just look, i don't buy)
So, in other words, you want to experience life as a local
while you're here. 
If you intend to commit gastronomical suicide and rely entirely
on Subway sandwiches as a means of sustenance during your stay
here, you could probably get by on $25 for three meals. Subway is
even running a deal in which they are offering a selection of their
"footlong" sandwiches for $5 each.
Bear in mind that, given the size of towns and cities here,
"walking around" won't get you very far. If you're going to be
staying with friends and/or relatives, chances are they'll be way
out in the suburbs where motorized transporation is a necessity to
get around.
