Slime boxes.

Slime boxes contain yellow and silver slimes that give AMAZING EXP for low level people. They are typically found in Fairy Tale Land in any channel, around the middle book, to the left a bit, theres a box with a maple sign on it, hit it a few times, and it should break, giving you 1 - 5M mesos and a bunch of slimes. Kill these and take the mesos for an easy start on Kudo MS.