When you choose a Discipline, it allows you to use every weapon within that group. So, if a character chooses Blunt, he can use a Morningstar, Club, Mace and Flail at the same ability. Just as in Slashing, they may use Broadsword, Scimitar, Great Sword and Shortsword.
To buy a Rank in a Discipline, the cost is exactly whatever Rank you are moving up to. So, if a character is Rank 4 and is buying Rank 5, it would cost 5 Skill Points.
Rank 1 = 1
Rank 2 = 3
Rank 3 = 6
Rank 4 = 10
Rank 5 = 15/ Bonus
Rank 6 = 21
Rank 7 = 28
Rank 8 = 36
Rank 9 = 45
Rank 10 = 55 / Bonus
Rank 11 = 66
Rank 12 = 78
Rank 13 = 91
Rank 14 = 105
Rank 15 = 120 / Bonus
Rank 16 = 136
Rank 17 = 153
Rank 18 = 171
Rank 19 = 190
Rank 20 = 210 / +1 Bonus
Rank 21 = 231
Rank 22 = 253
Rank 23 = 276
Rank 24 = 300
Rank 25 = 325 Mastery