A 12 headed zombie hydra created in a desecrated area with an alter is going to have 24d12 + 48hps +3 from toughness feat (195 hps), +19 attack bonus (+12 BAB, +2 profane, +7 str, -2 size) for 2d8 +9 (+7 str, +2 profane) damage per attack with 12 attacks/round, and a base AC of 25 (-2 size, +17 natural) with DR 5/slashing at a cost of 600 gps (24HD X 25 gp) which is less than 1% of a level 12 character's wealth and that's just core with no corpsecrafter feats or special items like black sand so those numbers can easily go up with a little effort.
By comparison a level 12 human monk with 18 str, 18 dex, 18 con, and 18 wis (being extremely generous) is going to have 12d8 + 48 hps (96 hps), +13 (+9 BAB, +4 str) unarmed attack bonus for 2d6 +4 damage with 4 attacks/round on a full attack, and a base AC of 20 (+4 dex, +4 wis, +2 monk bonus). Granted the monk can improve those numbers with feats and items but it's going to cost a lot more than 600 gps to do that.