I wouldn't click the link above it looks like a virus page.
Any cab starts at 25 pesos if it is a blue and white bug on the Costera. Don't use a port taxi unless you want to pay triple or more. It just is not worth it.
Walk to the street - hail a blue and white. You can hire many of the drivers for about 200 pesos an hour. And yes, any cab driver can take you any place a tour guide can go.
No. Acapulco is not unsafe unless you make it that way. Being on a bad street alone in the middle of the night drunk could get you in trouble. Other than that - don't worry. Acapulco people are really pretty cool.