Right now the rates for a hotel within walking distance is (minimum) $140, unless some hotels are evading my search; and then I found some about 15 minutes away for about (minimum) $70 a night. If you get a group rate then you can get them for less though, I do believe. That's judging the rates don't change by March, which I'm sure they will.
As far as parking? I honestly have no clue as far as parking goes for the Con, as bad as that sounds. xD I tend to walk there from my hotel if I can, and if not I take the MARTA and then walk from the station.