The item "Frozen Negg" has inflated in cost to around 340k NP - likely due to the upcoming plot, and the amount of neggery points these give.
(you need an account to see links)
The battledome opponent Snowager on easy difficulty (easy only, medium/hard will not drop it) has a chance to drop one of these.
On average one can expect about 8-11 of these to drop each month if you battle the Snowager on Easy every day for your drops. That's 2.7 - 3.7 mil NP a month from just these, not including the other drops like codestones you'll get.
This is more profit than any other non-premium battledome opponent at the moment. Not many people know about this, and most battledome guides you'll find online and even here will recommend other opponents for non-premium users.
Snowager is unlocked in the dome if you try to get treasure while he's asleep and are blasted.
Let me know if you get a frozen negg drop!