San Antonio

Do you mean San Antonio, a municipality in the Tolima department, population some 16,000 souls?  Or do you mean the barrio San Antonio in Santiago de Cali?

Cost of living is lower than in developed countries, depending on your lifestyle, of course.  You could figure approximately one-half as expensive as in a developed country, but in so many ways it's like comparing apples and oranges, or comparar peras con mangos...you give up some conveniences we take for granted, but you gain in other ways.

Single women almost everywhere are overall less safe from crime than men - in Colombia as everywhere, your behavior can often determine your susceptibility to being the victim of a crime.  The most common crimes single women suffer in Colombia are mugging/robbery/theft. 

Crime levels overall are higher in Colombia than in many developed countries, but with the caveat that there are many places in many cities in the US that are far more dangerous even if you don't stand out, than many if not most places in Colombia where a foreigner does stand out...

You can use numbeo.com to get at least some idea of crime and other things including cost of living, comparing two cities.  For instance here is a comparison between Brooklyn, NY and Medellín, Antioquia:

https://www.numbeo.com/crime/compare_ci … Comparison

In general crime will be less in smaller cities especially violent crimes but crimes like robbery/mugging are a possibility anywhere.  But you should not be guided by your fears, but look at things realistically and behave so as to minimize risk and loss.  You could do a search for
how to avoid street crime colombia
and find a number of articles/blogs that have some good advice.