One +1 Skill Tome is 195. Buying 6 individually is 6x195=1170. Buying as a 6-pack is only 895. By buying in bulk, you save 275 TP. Good deal, and usual practice to entice people into buying more.
Now look at +2 or +3 skill tomes.
One +2 Skill Tome is 295, or 1770 for 6 individually. However, buying a pack of 6 is 1795, MORE TP than buying them individually! And same thing with the +3s.
Something is wrong with the prices here.