I don’t know the exact value of IITs.
Many of my friends were in NITs and the minimum salary (CS branch) was 12 lpa for UG.
CS/IS/EC/IT salaries will be comparable.
For same branch IIT will be much more.
Also Government companies go for placements for these colleges according to what I Know.
Other branches it may be slightly less but in the long term, the brand name will equalize the salary range.
Good Luck.