Hi again, Laura,
I am sure that this must stand for "precio diferenciado", which is an expression that comes up very frequently in relation to Master's degree courses in Spain. Just google "máster" + "precio diferenciado" and you'll see what I mean.

What it means, to put it crudely, is "expensive". The system is that fees for official master's courses are set by the Autonomous Communities (each sets its own), on the basis of a price per credit. It's commonly of the order of 30-35 euros per credit. But universities are allowed to charge more than this, and some do. I think it's basically a market thing: certain master's courses are more in demand, and if they can fill them at a higher price, they are allowed to. But only up to a point: they can't charge more than 30% of the real cost of teaching the course (which goes to show that the standard fees are a small percentage of this real cost).

Master's degrees that charge above the official rate are called "precio diferenciado".

Here's a brief definition from one of the universities that does this, Carlos III in Madrid:

"3. ¿Qué significa Máster de Precio Diferenciado?
Significa que el precio por crédito de tu Máster es superior al mínimo establecido por el Decreto de Tasas de la Comunidad de Madrid para los Másteres Universitarios."
http://portal.uc3m.es/portal/page/portal/postgrado_mast_doct...

If you look at pp. 3-4 of this document, from Madrid, you'll see some real figures: Alcalá, Carlos III and Rey Juan Carlos have courses with prices per credit way above the official tariff of about 29-36 euros (depending on the type of teaching involved):
http://www.emes.es/LinkClick.aspx?fileticket=8SmjqvpJ6vA=&ta...

Here's a very useful fuller explanation in a Ministry document:

"5.2.2. Precio de matrícula de Másteres oficiales
Actualmente existen dos formatos de precio: Por un lado, los precios no diferenciados que están dentro de una horquilla de precios que se fijó inicialmente entre 13 y 28 €/crédito (y que posteriormente se ha ido actualizando según la tasa de variación del IPC) y la opción del precio diferenciado, en el que de forma excepcional el precio de matrícula de un Máster puede llegar a costar el 30% del coste. Sólo el 3% de los Másteres oficiales tienen precio diferenciado."
http://www.mecd.gob.es/dctm/boloniaeees/documentos/zonad/gba...

So how do you translate this? "Precio diferenciado" is a bit of a euphemism, I think, and a literal translation, "differentiated fees" or "differential fees", won't really be understood on its own. Maybe you could either keep the Spanish expression (in full) or give the literal translation in inverted commas, and add something like "premium rate" which would get the point across. Even so, you may feel like adding a note.

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Note added at 3 hrs (2015-06-04 20:15:47 GMT)
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It occurs to me that since you have the figures, you could confirm this hypothesis by comparing the cost of this course with the official rate for the Comunidad Autónoma in question. It would take a bit of research, but it could be done in principle.