Well since lottery is mainly about money, let's say that the prize is zeny.
Here is my idea for this, "autohost event"
The event shall be hosted twice a week.
The player pays an amount of zeny (Amount to be discussed) and gets a lottery ticket, ("such item cannot be traded or stored in the storage"), at a certain hour the NPC will announce the winner and the winner can trade his lottery ticket for the prize.
For the prizes I was thinking that instead of making players to introduce the numbers they want, the NPC shall auto-generate the numbers for each ticket and instead of having 1 winner, we could have 3 different winners.
Possible prizes:
1st: 3 Bronze Coins
2nd: 2 Bronze Coins
3rd: 1 Bronze Coin
What do you people think?