Changing vitz belt is not a big issue.As the length is bigger than other cars(1765 -1770mm) and a number of pulleys are involved, so try to get a good mechanic for the job.Carefully check the route of belt before uninstalling,because an unexperienced mechanic forgets the route and makes the job complicated.The prices are as follows.
4pk1765 or 4pk1770 Bando japan Rs.500
4pk1765 or 4pk1770 optibelt germany Rs.500