I recently hired a taxi at the Cartagena airport to take us to Santa Marta. The guy who took us has a side job as a private driver so he swung by his house on the way out of town and we switched from a crummy taxi to a new KIA. It was one of the nicest cars I saw in Colombia. I figured I'd post his info because he was great: (I'm not sure what all the numbers are I'm just copying from his business card)
Cells: 313 55 83 983 - 300 418 2190
I've seen on here a price quote of 250,000 pesos but I guess the price has gone up because the drivers at the airport laughed at that and wrote us a schedule for the bus. We ended up agreeing on 370,000 but had him takes us all the way to Costeno Beach for 540,000.