Hi Carlos,
Your English is fine. No se preocupe. (My Google Spanish...)
If cost is a factor, maybe look on the http://ArduinoInfo.Info WIKI and
http://arduino-info.wikispaces.com/Nrf24L01-2.4GHz-HowTo
There is a multidrop network project here: http://maniacbug.github.com/RF24Network/index.html
Some example hardware here: http://goo.gl/Bn9fw (Widely available elsewhere too)
DISCLAIMER: Mentioned stuff from my own shop...