Forget about buying for a moment, you need to seriously offload some dead weight.
Granero, Lass Diarra and Hamit Altintop for starters, as Real have WAY to many midfielders. If, however, you plan on utilizing a 4-5-1 formation, then possibly keep Lass.
If you want another top class striker, go for Seydou Doumbia. You can get him for around 16 mil pounds, and he is easily one of the best strikers in the game.
In the central defender department, if you think you need one, your first choice has to be Salvatore Bocchetti from Ruben Kazan. Don't know how much he will set you back, but he is a class commanding defender, and relatively young.
If you are looking for back-up for Marcelo/Coentrao in the wing back position, you will want to look at another Ruben Kazan starlet in Christian Ansaldi. Good utility man in defense.
I think Real Madrid only needs a ST and a DLR backup.
As ST, as someone mentioned, get Doumbia, put all your creative players with trough balls to often and get ready for a season full of goals.
As for DLR, you may get a world class DR which is Darijo Srna. Not the best value/money because he is a bit old but he'll be one of the best DR's in the game for 3 seasons (got him for arround 15M€-17M€ on my Arsenal save). Ansaldi is good for backup, as someone mentioned. I always find good DLR's a bit hard to find, they are usually rare and expensive.
Unload all the dead weight you have (after choosing tactic), it will give you a lot of money.
Dede or Kurt Zouma (you have Verane, Albiol etc already) Javi Martinez (not sure if he will come though) Inigo Martinez, Iker Munian (play outwide as well) or Sebastian Corchia/Cesar Azpilicueta as right backs (they are brilliant for the future and can start immediately) See if you can get Fernando Muslera (he just joined Galatasaray, but may leave for Real) Volkan Demirel, Rui Patricio as backup keepers (Rui is quality) if Iker gets injured etc.. Jefferson is also quality!
You do not need a striker at all, Benzema and Higuan are quality as well as having Ronaldo and Callejon who can be retrained very quickly!
(already mentioned above) Keep Lass! sell off other fringe players and free up wages!
you just need a good backup keeper, a good young CB like Zouma, Martinez to train up and get ready and a RB