this site
[broken link removed]
seems to indicate it's a 60 minute journey using 2 metro's and a train,
not sure on prices but it seems an easy enough site to navigate.
Driving it's motorway all the way (take the M40 motorway from the airport don't cut across the city) - Not too difficult and fairly hard to get lost .. I don't know Las Rozas but I have driven from Barajas airport and out the A6 Motorway towards the North West several times .. and this motorway goes right through Las Rozas