3000 bucks per exam is a surprise. How can the institute afford it? Anyways, this is a question for which I guess the institute can provide an answer. Generally when we get a coupon, it is for a particular exam. So, if you have 3 coupons, it should be one for each exam. But just check up with the institute.
I do not know what kind of tie ups SUN has with institutes so far as the coupons usability and price is concerned; but I do not see a reason for it to be 'a lot' different than what a person gets if he purchases it online. Not even heard of this.
We have different forums for SCJP, SCWCD and so on. If you are planning to appear for SCJP, please post your SCJP related questions in the SCJP Forum