If you make your search using other webpages, please note that the conference takes place in San Lorenzo de El Escorial. Just El Escorial is another municipality (where the train station actually is), 2 km down the valley. Most hotels are indeed in San Lorenzo de El Escorial but it is advisable that you make sure that your hotel is on the spot.
A list of restaurants can be found in http://empresas.sanlorenzoturismo.es/restaurantes
You are free to make your own travel arrangements through whatever methods you wish to.
The cost of a taxi from the airport to the conference location is around €90.
The local organisers, in order to offset the costs of the transfer from the airport to your hotel, have contacted a travel agent that will arrange the transfer for free if you book through them. There are other ways to travel between the airport and the conference venue. Mundia Viajes, the travel agent, can help with your travel arrangements. They can arrange your hotel at San Lorenzo de El Escorial, the site of the conference, as well your transfer from Madrid airport to the venue.
They offer packages (flights + transfer + hotel) as well as individual products. They can be contacted via firstname.lastname@example.org
Note: Other travel agents exist, and may provide similar services as Mundia Viajes.
RCU (the conference Venue) has 15 rooms (till 27th morning, three of them have 2 beds). Breakfast and WiFi included. You can book them by Mundia Viajes (email@example.com)
ITS has arranged special deals through the Complutense University of Madrid travel agency. Special prices for hotels downtown Madrid: Hotel EXE Moncloa; T3 Tirol; NH Alberto Aguilera; NH Arguelles have been arranged (breakfast included). Participants who want to book those hotels, should send an email to firstname.lastname@example.org and email@example.com (in copy).