Let's not forget the high risk of cancer from the solar radiations. Also an almost one-year travel can't be done in a ship that's like a crowded airplane. We'd go crazy without some more space and intimacy (and work to do).
Not that it's impossible but escaping the Earth's gravity cheaply isn't the only challenge.
There are over 5,000 crew members of nuclear submarines in the USN. I think they currently only have 90-day deployments, but I don't think they would tell you that 1 year travel "can't be done." It's a matter of motivation/necessity I think.
Not that it's impossible but escaping the Earth's gravity cheaply isn't the only challenge.