As far as the discount code, have you joined the MSPA yet? Membership is required to obtain certification, and I think when you join you get a code. I think the discount is the cost of the first year's membership in MSPA. This is where I found the list of certification classes, and there is a link on the page to join, directly under the list of classes, where it says "Certification Courses (membership is required to obtain certification, click here to join)"
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www.mspa-na.org]
There is also a link on that page to the Certification Frequently Asked Questions.