The Aeropuertos Argentina website lists this taxi operator at PSS. Their direct site is here.

I'd suggest calling them up or sending them an email and asking for a price quote. I highly doubt you'll find someone there with great English skills, though.

My expectation is that the cost will be somewhat high (although 100 quid really does sound excessive), given that it's an international trip and the driver would then have to get back to Argentina. By public transportation it would probably be a handful of dollars, but of course that would be a rather more complicated procedure, especially if you don't speak Spanish and/or have lots of luggage.