This isn't exclusive to swtor, many many games have stupidly priced items because of rarity. Its like in csgo if you have a 1/1 Karambit MW Stattrack Slaughter worth 2 Million Euros, but the game just decides to sell them in the store for 15Euro's. 2.5 Billion is by no metrics a small amount of credits, but its not really that much either. There are also several helmets that are identical to the destroyer helmet and for a fraction of the price, The destroyer set is a collectible, for those who like to collect entire armor sets and all of the ones in the game for that sake. In my case, 14 year old me thought the destroyer set looked sick and bought it for 600 CC when it was available. But pains me even more is that i deleted several of the pieces of my destroyer armor, only leaving me with the boots, belt, Chest piece and helmet.