When a contract is added to a student record, allow the tuition field to override the tuition amount in the contract. Maybe make this a setting to "allow individual contract tuition override", or something.

There are always a few "special" students who have one-off tuition amounts. For example: an exchange student, here for three weeks, and our agreement with their sending school specifies how much may be charged.

Creating a whole new category of contracts for one student is both ridiculous and makes it very difficult to manage. Having a contract category for "Exchange Students" would make much more sense.