Where did you read that?
You can walk into I-Day with zero money and be fine. That said, I'm sure it helps to have a bit of money for the summer -- nowhere near $1,000 let alone $3,000. I don't think plebes get much MidStore time during PS so there's no place to spend their money except maybe the baseball game, if they get to attend one. During Ac Year, it's nice to have "walking around money" for MidStore, Dahlgren and going into town. However, there are more than a few plebes who come from impoverished backgrounds and show up with zero. Remember, plebes will be paid. They don't see a lot of that money in the first year, but it's more than enough to get by.
You may be confusing this with the requirement years ago to bring money on I-Day for the ACE loan. That requirement no longer exists.