Authorize.net Implementation Expert

Have an existing site that has used [login to view URL] for many years. Need two changes: 1. We are currently using the Weblink connection method and we need to convert our connection method to either the Advanced Integration Method (AIM) or Simple Integration Method (SIM). 2. Also,we need the following corrected: a) When someone goes through the registration process on our web site (putting themselves into our Windows SQL 2010 database) they are then sent by link to the [login to view URL] page where they pay. b) If they DO NOT pay for some reason, (for instance; if their payment is declined, or if they simply log out after filling out the registration form) all they need to do is go back to our home page and login and they are able to access their program, without having paid for it, as they have already put themselves in our database. We need a way to keep students who have not paid from accessing their program. I am on a frighteningly tight budget and I am looking for a database/[login to view URL] expert who can implement these changes as professionally, economically and seamlessly as possible. Freelancer will be chosen from bids Friday 3/9. The work is to begin 3/12/2012.