MLG uses some rock instrumentals in the last couple of events. Are they known? They may not be the best music ever, but kind of liked them as background for starcraft.
I think the best way to do this would be to strike a deal with one major recording company. It limits your selection, but at least you have one, and can hopefully avoid unmanagably high costs in the process (or maybe not, I really have no idea.) But the music labels would also be benefiting from this too... it just gets the music out there. I mean, look at songs that Day9 reccomends on his twitter... they go up like 5k views in a couple of hours...
Pride, Dream and K1 have the most badass entrances. UFC entrances have always been so bland. This SICK DUDE alone trumps any UFC entrance I've seen, and he does it multiple times.
Of course, a lot of the additional costs as well as the effort has to be has to be taken up by the player and/or his sponsors. Not probably doable, but one can only dream.