Salary comparison
Today TOI article shows median IIT placement salary at 20 lakhs. Note this is CTC. Take home after income tax will be around 60% of this (best case scenario) which means take home salary will be 12 lakhs p.a.
So cost after passing 12th = IIT classes + 4 years IIT cost ( i don't know amount) you will start to earn 1 lakh p.m. Time taken 5 years approx.
If someone joins as a cadet - 1year pre-sea training 8 lakhs- start earning 30,000 pm for 18 months cadetship total earning 5.4 lakhs. Exam cost - 5.4 lakhs (max) - so yr cadetship pays for exam. 3rd mate salary 3600USD - 3.4 Lakhs per month. Tax free . Work for 7 months = almost 35 lakhs take home salary + 5 months leave per year.
All this is ASSUMING you're intelligent enough to crack IIT. Even then Merchant Navy pays more.
Think about it.