Costs are spread over 20-30 years of the life of ships. GDP and hence defence expenditure growth and soft loans to buy ships all need to be taken into account.
No offence but hot are using schoolboy maths here.
IF someone will loan you a 3 billion dollars soft loan paid over 30 years then sure, but such a loan can only come from another government but no one in their right mind is gonna loan you 3 billion for ddgs, ships what would effectively be white elephants, military ships do not generate a return(unlike a power station or a port) outside of the immediate shipbuilding business, and if there is no interest or interest that does not keep up with inflation then there is no economical reason, so the only thing left is a political loan, however in any scenario involving bangladesh, a loan for subs/sams/jets makes more sense than 3 DDGs. if your potential enemy is india, then DDG will do no nothing aside from taking fund away from the army, yea you'll be real free alright, roam the ocean all you want while the indian army occupies all your land(if the indian navy dont sink your measly 3 DDGS first). if your potential enemy is myanmar, they barely have a navy to speak of, a force of corvettes/frigates and a strong land force is more than enough. if your potential enemy is the us, then 10 DDGs won't help, let alone 3.
again what bangladesh need is something to play on the enemies weakness, not their strengths, that means get subs, and anti-air, jets, things that are hard to kill, difficult to find and punch above their weight, to defend the homeland, buy time, make it expensive to attack(not necessarily to win), NOT take the fight to a much stronger enemy, make friends that can help you if a potential enemy attacks. for example, india would have to be off the deep end to attack if the front line have say, 5000 americans or chinese for that matter (either civilians or military staff that will get hit hard first).
