Edmonton already has ~4.5 million in dead cap space for next year with current buyouts and retained salary. If they buy out Neal, that jumps to ~6.5, not to mention the inevitable Koskinen buyout once Edmonton does what Edmonton does to goalies.
Having said that, Edmonton had no choice to trade him, for the reasons stated above, they just couldn't afford to buy him out, they couldn't afford to keep him, and he just wasn't a good fit.
While it wouldn't be ideal, Calgary even with a Lucic buyout, is at ~7.5 in dead cap space, but that's not going to happen, Lucic is exactly what this Calgary team needs and he's going to be an important part of its success. Calgary is just a much better fit for him.