The most economic and powerful mode of marketing is Word of Mouth Marketing (WOMM)

Nothing can beat this WOMM and because its suggested or told or promoted by nearones/dearones to others it has its max reach with trust. That too you a app for MUSIC, liked by everyone.

With this modern world after Social Networking sites came in everyone forget this WOMM but even now WOMM wins.

So try this with zero cost.