student loan interest rate 一般是多少? depends on the type of loan

The post above gave you the interests of most common loans - Stafford and Perkins.  However, there is a catch.  These loans are only offered to qualified students and there are annual limits. 

You mentioned $20-30W.  That means you plan to borrow full prices for a private college.  I don't think Stafford and Perkins will cover that much.  You will have to get plus loans and other private loans with higher interests.

This is the first time I have even seen anyone who will borrow the whole amount.  I don't think any university worths that much debt. 

What is your situation.  May be you should first try to understand the FA system first.