Match Checkout fields with Gateway fields

Using a plugin for an online store but the fields on the checkout page do not match up with the fields on our payment gateway. We need to have the name for each field to match on both so that the information gets transferred from our store to our gateway. I have what each field needs to be named, but need someone that knows how to change the code so that it does not break! Currently it names each field as e.g. name="collected_data[3]" but instead should say name="email" so that it matches with the payment gateway. The stores uses the wp-ecommerce plugin and wordpress. The payment gateway is FirstData, and I have the manual that contains all of the correct fields. MUST know Wordpress, and MUST have previous experience with payment gateways and eCommerce. The budget for this project is up to $150.