Add donations to donation levels

A user can choose to donate at a specific donation level for a specific project. 
The donation amount, associated donation level, and donating user id are recorded in the database.
Instead of hidden fields, what if you nest donation under level? Then you can:

1) Grab the level based on the ID in the URL
2) Pull the amount from the level

Otherwise I think people could change the amount to 0 and keep the level the same and they'd pay $0 but be marked as contributing to the $200 level.