I live in a one bedroom apartment so pretty much everything is bought on an 'as needed' basis. lol However, that said, you have to have salt. So, I buy a bucket at a time, and, with only a BioCube, that lasts a long while.
ETA: When I first set up this particular tank I thought I'd go with pre-mixed water from my LFS so that I didn't have to even store salt, but then, of course, you have to take the salt they are using, which is IO, and I don't care for IO, so I 'made room' (aka - I put my bucket of salt in the closet-area that holds my heater - shhh, don't tell Maintenance!) and started just bringing home RO from the fish store.