Each Great Nature sells for 1500 zeny normally, while each green live sells for 500 zeny (w/o OC bonuses). Example: 10 GN would sell for 15000 zeny, but 60 green lives sell for 30000 zeny, thats if your luck is terrible. This is one of the reasons why monks stay at sleepers for forever.
Monk Leveling Spots 75-99:
Besides the great options mentioned by Linnea, Stalactic Golems one north of Comodo give decent exp for occult/investigate monks, and also have a decent elu/rough elu drop rate if one needs any in this mining world.
