Money.

Riiiiiiight... so Garret wasn't exactly the richest boy in the Wizarding World, nowhere near it, but it was a trivial matter. He'd just use his Quill money and then borrow a Quill off Cela for the exams, it wasn't as if she was about to let him go into the exams without a Quill!

"No worries," he grinned his devil-may-care grin down at her as he tossed a handful of Chocolate Frogs over the pile, "I've got it sorted."