First of all: You get what you pay for. Cost of living in Chile differ greatly. If you want to live by western standards I'd say cost of living is even higher. However, if you don't mind an old house and buy your necessities at local markets you can get by a lot cheaper. I know a lot of Chileans who get by with 300.000CLP.
For renting property in V Region check out
http://www.portalinmobiliario.com. Might be good for other areas, too, but I never checked. You can get decent places below 200.000 CLP (400 USD) if you don't need north american standards. Most properties are also listed on vivastreet.cl, prices are usually negotiable.
As you go further north, things get more expensive. Valparaiso is probably still the cheapest area if you don't rent around the Unesco hills.
I've been living in Concón for a year now and it is not cheap. It's also pretty boring.

Except for the view I can't really recommend it. I'll be moving back to Valpo in a few weeks.