Today's storage is more expensive than in the past normally because most 'hard drives' are now much faster and more reliable. They no longer have a spinning disk but are made from high-speed electronics, which is particularly expensive in the very large sizes.
Take a look at your existing system and see how much of the 1.8TB is being used. Probably no more than 300 GB. Unless you really need more than 512GB, just stick with that. Should you really need more, is it just for long-term storage? If so, buy a large external hard-disk and keep the long-term stuff there.