I have used Ziptransfers on a number of occasions and have been very happy with the service. We tried to book a transfer from Buenos Aires city centre to the airport on the day before we were to travel. Having gone through most of the booking procedure I was informed that because there was less than 24 hours, I had to ring an Irish number which I did. I was then given a rigmarole of instructions about having to wait for further confirmation and quoting reference numbers so I terminated the process. I found another online airport taxi transfer company which dealt with my request quickly and efficiently and provided an excellent driver. Incidentally, their quote was cheaper than yours.