San Fernando hitch point.
It's cheaper to just get the train from Atocha to station San Fernando which is nearby Madrid.
Behind the San Fernando train station there is an entrance on the highway motorway where you can easily hitchhike from.
I really liked the spot because it's a few kilometers away from the landing track of the Barajas airport and you can see/take pictures of airplanes while they are headed for landing ( 50-100meters from ground ).
The train ticket to San Fernando costs 1.45 euro.