Indian organisations are notorious in having extremely low estimates that later blow up to 4-5 times. So while I have more trust in ISRO (Indian Space Research Organization), their numbers might be off by a factor.
For example, check the projections on the James Webb space telescope and see for yourself how the costs doubled and tripled. IMO we shouldn't look at it in terms of those costs; even if double and tripled they are not that high. Look at their effect on the larger picture.
"The project was scheduled to be completed in 1998 at an estimated cost of $2.8 billion (in 1982 dollars, US$6.0 billion adjusted for inflation as of 2006).The project was not completed, however, until December 2007, at a cost of over $14.6 billion ($8.08 billion in 1982 dollars) as of 2006. The Boston Globe estimated that the project will ultimately cost $22 billion, including interest, and that it will not be paid off until 2038."