Galway-Blow seems surprised that you can rent an apartment for €350 per month during the off season. You can and you can even get an apartment cheaper if you do some more work. But, you will be charged for utilities (water, electricity, refuse, public lighting, community fees etc). So before you decide to jump on the first plane out of Dublin for Portugal or the Costas - Stop - Think - Ensure what you thought you were buying is what you bought. Play safe and do not look a gift horse in the mouth.
The biggest mistake some people make on wintering in Portugal/Spain is renting in a ghost town. These towns are flowing with activity during July and August and nearly shut down completely come October through to May. If there is no good public transport service you may need a car even for the weekly shopping.
The going rate in a non-ghost-town good resort is €650 per month + electricity cost (circa €100.00) for a good two bedroom apartment centrally located. All the services are nearby, supermarkets, shops, restaurants, public transport, wi-fi, beach, level walks etc. Don't scrimp and pay dearer later, know what you are buying.