Traditionally the reason a country becomes 'cheap' when their economy takes a nosedive is that their currency generally also takes a nosedive. That happened in Iceland in 2008, when the Krona halved in value in a few months. As prices did not increase to match, people visiting Iceland in late 2008 or early 2009 experienced vastly cheaper prices in 'real' money terms.
The difference here is that the countries you name are all in the Eurozone, so they don't have their own currency. So long as the far larger economies of Germany and France remain stable, the Euro will remain stable. That means that your dollars or pounds will still be worth about the same as before, so things won't suddenly get cheaper by default.
That said, when economies are under strain, some prices may be lowered out of desperation- better to get less for a hotel than nothing at all. Underlying this, real estate prices in Spain and Ireland have collapsed. Good news if looking for a holiday home, but don't expect your hotel cots to suddenly halve.
So where to go? Well, regardless of the financial crisis some places are cheaper than others. A June 2010 survey into destinations (see bottom link) showed big differences in real costs, and mentioned one of the countries on your shortlist as one of the best value destinations: Greece.
Greece's economic woes certainly won't have made it more expensive since then, so it is undoubtably a good choice, as is Cyprus.