If you don't have any luggage than local is the best option for you. From Kalyan board any fast/slow local going towards Kurla/Dadar/CST and deboard at Ghatkopar,take a metro and get down at Airport Railway Station or else you can take auto from Ghatkopar stn as well.
No taxis are available from Kalyan to Airport. You will have to book a private cab which would cost you around 800-1000 rs.