You are correct. It depends on your character level how much it costs to unlearn a skill, increasing as the square of the level, and is independent of how many skill points you put into it. If you select a skill and click on the 'unlearn' icon, it will pop up a message saying how much gold it would take to do so.
Cost = (200 / 3) * L^2 [color:"#3A495A"].......[/color](rounded down, if necessary)
Level [color:"#3A495A"]0[/color]2 = 266 gold [color:"#3A495A"]0[/color]
Level [color:"#3A495A"]0[/color]3 = 600
Level [color:"#3A495A"]0[/color]4 = 1066
Level 30 = 60,000 (?)[color:"#3A495A"]......[/color] (assuming the same pattern holds)
Level 51 = 173,400 (?)
This is based on just 3 levels (only got to level 4 in the demo), so there could be a cap at some point, or it could go up faster at higher levels. Also, this is subject to change in the full game.