What's the cheapest city in Colombia for food and lodging that's still safe?

I am a 32 yr old single male looking for some pretty ladies and looking to vacation in Colombia. I don't know which city to go to. Cartagena, Medellin, or Cali. Which one is the cheapest and safest? I know Cartagena is the only one w a beach, and I do like going to the beach. Please tell me your opinions. Thanks.