It depends on the person or family. Everybody's different and may have different 'nessesities'. Also, depends on where you want to live, some places are more expensive. Do you want to live in a trendy area like say, Renaca or Las Condes ?
Arica is in the far north of Chile, my basic expenses there for an apartment, gas, water, electricity, Internet, and gastos communos was, IIRC, about 325USD per month. That's not including food. Check my back posts I made a thread about my bills. Check out TomBrad2's blog for all the Arica info:
http://infoarica.blogspot.com/ Tomas is a good guy to know. Arica is not for everybody I guess, being in the north, but it's a nice place and has the benefit of being pretty cheap to live there.
Are you single? You can find cheap in Valpo, but you may not want to even let your dog live in it. As a very rough estimate you'll pay 150k+ CLP per month to get a somewhat liveable place. But even then.... be careful. Think more like 175ish to 200. Apt and house hunting in Chile is a
HUGE subject with an amazing amount of twisty 'gotcha's'.
Don't burn any bridges. Chile may not be for you. Check it out for awhile first. Chile has frustrating things about it that for a gringo take getting used to, in other words it aint a paradise. That said i wish I was there now.
Assuming your single have at least 10k-12k USD before you go. It may be difficult to make in money in Chile, again that depends on the person. I know it's time consuming but there is a lot of good info on this forum. Take some time to read all the old threads. You'll be better informed about what to expect.
cheers.