Authorize.net integration from a landing page shopping cart

We have a web site, www.immigration-revealed.com. It has a shopping cart design (not an actual cart) to allow for integration with authorize.net. We currently on another URL have people go to a second page for the purchase, which is the [login to view URL] secure page. What we want to do is have people fill out all the info on our landing page and then integrate it with (AIM) to authorize.net. We have secured our own server on [login to view URL] for this. We are also considering purchasing [login to view URL]'s shopping cart if that is what we should have on the landing page to make it easier. We are new to shopping carts and want to find someone trustworthy and knowledgeable to work with as we have more than one project in this arena. We are looking for someone who will explain what needs to be done and also do it in a couple of days at a fair price. We are looking for a long-term relationship with a developer. In summary, our goal is to create a number of landing pages starting with this one where the people place all their info and then it is integrated with authorize.net. Authorize has a package that includes sample code etc to make it easy for you. We are just unsure of how the HTML page works and whether we should also implement an external shopping cart. For example, some of the items need drop-downs and we also want to have a google shopping cart as well as paypal as payment options.