So I'm thinking about buying Nier for my ps3. How much storage does it take up?
According to this thread, the install size is just 4GB, but it's optional.
After going home, I checked my own NIER disc and it appears that the amount of required HDD space is 7111KB, so less than 1GB.
According to the PS Store listing for NIER, this game is disc-only, so digital download is not an option. 7111KB is all that you need, with an extra 4GB being optional.
From experience, though, you should have 20% or so of your HDD free if you want your games to run well. Running games when you have extremely little storage remaining causes games to perform very poorly.