I noticed that leveling up skills might get a little confusing so I decided to post a chart here for your viewing pleasure and for easy access. I would also like to note that the cost of the SP is to level the SP, and the uses are overall total uses, so they do not reset.
The Format will be like this:
Level: Base SP (The original Cost of the Skill) + (Number of SP required for that level) / Uses
Level 1: Base SP + 0 / 3
Level 2: Base SP + 0 / 6
Level 3: Base SP + 5 / 9
Level 4: Base SP + 5 / 12
Level 5: Base SP + 10 / 15
Level 6: Base SP + 10 / 18
Level 7: Base SP + 15 / 21
Level 8: Base SP + 15 / 24
Level 9: Base SP + 20 / 27
Level 10: Base SP + 20 / 31
Level 11: Base SP + 25 / 35
Level 12: Base SP + 25 / 39
Level 13: Base SP + 30 / 43
Level 14: Base SP + 30 / 47
Level 15: Base SP + 35 / 51
Level 16: Base SP + 35 / 55
Level 17: Base SP + 40 / 59
Level 18: Base SP + 40 / 63
Level 19: Base SP + 45 / 67
Level 20: Base SP + 45 / 71