I have never felt more ripped off by taxi drivers than in Manuel Antonio. Very simple though, insist with any red taxi anywhere in the country that they start their meter when you get in. By law they are supposed to do this, its when they don't that people start to get ripped off. If they refuse to do this ask them what the taxi number is and report them to the company, they will comply, they know exactly what they are doing.
Last time I was there one tried to charge me $10 for a $2 ride, I told the driver he was out of his mind, that I have lived here for 15 years and knew the law and my rights, asked for his taxi number and ID - Long story short I got my $2 Taxi.
If they refuse to turn on the meter find another taxi. I will say I have no idea where the hotel is where you are staying, my advice is taxis in general.
Cheers and good luck