Sir.. many of the operators like VRL, Neeta offer split services in Chennai-Bangalore-Mumbai route.. the buses that depart frm Mumbai proceed towards Bangalore and again continues their journey towards Chennai. They will cover the entire journey in 24hrs b/n Chennai and Mumbai and they charge little over 1.5k. Many of my frnds who are not able to get reserved ticket in dedicated trains b/n MAS-CSTM, do this quite frequently.