Add this code and don't worry. Only adena in the drop list. Less memory without magic.
NpcTable.java
if (dropDat.getItemId() != PcInventory.ADENA_ID)
continue;
If you need something more you need things:
Be a Customer aCis and take this code; Buy this code from me (5 euro). Joke. :happyforever:
You can add GM Shop without NPC, by command /shop. Also not need add new multisells - only items list by categories. Price = Item Price * Rate Adena. Ofcourse, if you will be use adena as basic exchange item.