What is the Total Cost on the scoreboard?

Total Cost is the sum of the Buy In + Rebuys + Addons (if any).

So if your game Buy In was $20 and you had no Rebuys or Addons it would be $20.

If your Buy In was $20 and you had 2 Rebuys at $10 each and 1 Addon at $10 it, your Total Cost would be $50.