Voucher system for events


I'm trying to get an e-voucher plugin that generates a unique voucher number once the buyer has paid for it. Ideally the voucher numbers are pre-defined so that I can then add them as promotional codes for events using the events plugin for my client's site, or if there's an alternative around it then please do let me know.

I'm not sure if the question makes much sense, so I'll break it down into a structured format.

1. Person buys e-voucher that entitles them to x amount (in money or percentage) off an event.

2. Once bought, the e-voucher generates a unique number (either pre-defined or automatic).

3. The unique number can then be added as a promotional code to get a discount from events.

I do hope that clears it up a little and I'd appreciate your help. Currently my client is geared towards going for Event Espresso but if I can find a more suitable and affordable alternative then that would be fine.

I look forward to your response.