747--
There is very little serious crime in Costa Rica, to speak of. According to the US State Dept., the biggest crimes are mugging and theft. (
http://usembassy.or.cr/osac.html) The threat of terrorism or violent crime is "non-existant". The biggest risk is that they lie in an Earthquake zone.
I think for the cost of living, you can't beat it for retirement. (I will agree, though that for just relaxing on the beach in a five-star hotel with full amenities, the Islands are probably a better bet. Just a lot more expensive.)