A good idea for a money sink would be guild housing. You could make real estate in better zones such as Newland City or Omni Trade cost alot of credits and better stuff such as shop terms and insurance terms and grid terms cost money to get. You could improve the houses in many ways with more money and could sink like 100 billion credits into a guild house before you had everything you could possibly have. This would be a great way to get money off high lvl characters.