Because, as I said above, the price is not credits, but Tech Fragments. You earn these from various content-related things (completing Conquest, Mek-Sha Tradehouse mission weeklies, earning Renown levels, and many other things), as well as by deconstructing level 75 gear on a level 75 character. You can see how many Tech Fragments you have in the Currency tab of your inventory.

But also: