You can probably do better than that if you really try to game the promotion. Their certificates are non-refundable, but they are exchangeable. So, technically, you can use any of their certs as payment toward another one. E.g. buy $500 worth of certs using $400. Then buy another $500 using $400 of your last batch (ie. no additional investment), etc, etc. Theoretically, you could grow it without a limit. While I didn't see anything in the terms and conditions specifically against that, I would imagine they'd catch on and shut it down. However, you might be able to do that a couple of times and still stay under the radar.