one ofthe best classes in the game, why not have one in your party? If you have two in party of four, you could easily gain XP without searching monsters. First druid is fighting with party member. Second cast last breath to the loser. Swap positions. You need about 10 normal encounters to reach next level. Fighting one-on-one with equally powered enemy is considered deadly encounter and grants four times more xp. So in cost of 1500 gp and three 4th-level slots you could gain next level. Sure it has nonzero cost, but you need not perform complicated logistics to search quests, quest monsters and dungeons. Once party druids get 4th levels spells the party would level up quite fast.