It depends on what is being set up. If it's something like an internet connection, this might be the best option.

set up fees = what one pays to establish a new service

As for the suggestion of "precio establecido," this would be fine if the term to be translated did not include "set up" (which has a slightly different meaning from that of "set").

set up
3. To establish; found: set up a charity.
The American Heritage® Dictionary of the English Language, Third Edition copyright © 1992 by Houghton Mifflin Company.

Both Mike's and my suggestion reflect our common understanding of "set up." Though in this context it's used an adjective, modifying "price," it's related to the two-word verb, meaning to establish something, in this case, perhaps, a service contract (between a potential client and a telecommunications provider).

I hope this helps!

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Note added at 2 hrs (2009-02-15 20:27:03 GMT)
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Excuse me: that's "...used as an adjective..." :-)

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Note added at 2 hrs (2009-02-15 20:49:06 GMT)
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Otra opción puede ser el "precio inicial" (el cual viene siendo el precio para establecer o iniciar el servicio).

This is my understanding of "set up" as a native speaker of English.

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Note added at 3 hrs (2009-02-15 21:37:23 GMT)
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Hola Claudia: Estoy de acuerdo contigo en cuanto a "precio inicial" (si el contexto, en realidad, no tiene nada que ver con ninguna conexión como tal). :-)

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Note added at 4 hrs (2009-02-15 22:39:02 GMT)
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Resultados 1 - 10 de aproximadamente 611,000 de "set up fees". (0.28 segundos)
http://www.google.com.mx/search?hl=es&client=firefox-a&rls=o...

Resultados 1 - 10 de aproximadamente 143,000 de "start up fees". (0.20 segundos)
http://www.google.com.mx/search?q="start up fees"&ie=utf-8&o...

set up fee = start up fee (depending on the company)= cargo inicial
fee = cargo/comisión (en un banco)
charge = cargo
price = precio

FINAL SUGGESTION (en este contexto):
set up price = precio inicial

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Note added at 4 hrs (2009-02-15 22:47:34 GMT)
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Hola Claudia: Sí, me parece la mejor opción, which is why I just posted it as my final suggestion.

Saludos desde Oaxaca, México :-)