This strategy is quite innovative, but I feel some initial trepidation. After some thought, here are some drawbacks:
It suggests you're not providing the lowest possible price because there's money left over later if they buy enough. In other words, you're telling a price-sensitive market to wait to save money.
It requires customers to provide information that they might feel uncomfortable disclosing (events list) and that may be indeterminate.
IMO it feels like a "hard sell" for the other events, and that turns me off a little bit.
If customers aren't sure if they'll need more printing for those events, it voids the benefit. Even if they miss one, the perception is they've lost the loyalty reward opportunity.

You're not targeting a market that is looking for innovation so much as, as you point out, low first cost. Nor is it a market likely to engender loyalty, both because the product you provide is a commodity (from the customer's perspective) and college kids just don't think that way. Seems like the best way to create repeat business is to include with purchases a discount on future purchases made within the next x months (e.g. 6), or quantity discounts that include multiple designs so that they can preorder for multiple events (very unlikely, but might be worth a shot).

Best of luck.