Part 58: Prism gives us a run-down on Magic Experience
He's really not kidding. Here's the costs.pre:
Level 1: 0 Level 16: 10768 Level 2: 15 Level 17: 12661 Level 3: 26 Level 18: 14584 Level 4: 61 Level 19: 16514 Level 5: 133 Level 20: 18434 Level 6: 266 Level 21: 20340 Level 7: 494 Level 22: 22236 Level 8: 853 Level 23: 24131 Level 9: 1383 Level 24: 26041 Level 10: 2115 Level 25: 27986 Level 11: 3070 Level 26: 29989 Level 12: 4250 Level 27: 32071 Level 13: 5642 Level 28: 34258 Level 14: 7218 Level 29: 36574 Level 15: 8941 Level 30: 39043
Every character has one skill that levels up with magic XP, except for the mages who have two. Ronfar is one of those.
Also, it costs 15 MXP per Hiro's level to save the game.
edit: Also you don't get skills even CLOSE to every level; there's nothing between 1 and 8, for instance.
New skills are gotten (or a skill upgrades) at 1, 8, 13, 14, 16, 18, 21, 23, 27, 28, 29 and 30.