It really depends on the condo I guess. The condo I'm staying in now, although concrete walls et al, has a horrible main door and windows, soundproof-wise. And we're not allowed to change the door, as stupid as that sounds. Windows, well, they have to approve if I want to change it for the better. So you'll probably run into dumb things like that. But I suppose you can keep costs down if the condo is built well enough. I'm not an expert, but do know that sealing every crack in the door is pretty damn important, as well as a solid core door. And if the windows are fairly new, like the pvc Kenneth&Mock or Duralco, they're pretty airtight if the glass is thick enough.
Might be a good idea to describe the condo in detail, like where the piano will be and what the walls, doors and windows are like. Then the experts here can probably give some better advice. It is doable though.