Coupon function added to CRE LOADED site

I have a customized 1 page checkout CRE Store. Currently it does not have the coupon function implemented into it. I need the coupon function to be added to the site /[login to view URL] page, whereby people review their shopping cart and at the same time can use the coupons they have without having to login. I believe this job will not be difficult for someone that knows what they are doing. We need this very urgently so 3 days is a strict deadline. Please do not place bids unless you are 100% confident and certain you can meet the deadline. If you are late, I am sorry but we will not pay you. No excuses would be accepted for the delay.