Authorize.net set up (not shopping cart)

I have a client with [login to view URL] account set up for receiving credit card payments. Client provides services and wants to have a website payment platform to pay one-time invoices. This is not a shopping cart! I need and experienced eCommerce programer who know how to use [login to view URL] API's and can help decide which one will work best for this application. Requirements: 1. Build a simple form with required fields for credit card payment. 2. Integrate proper [login to view URL] API 3. Test until working perfectly. NOT REQUIRED: - SSL (already installed) - Design (plain form will be fine, no need to for special design) Payment terms: 100% milestone to be released up completion Time-frame: 1-2 days Start: Immediately