Secure Forms Built Around E-Commerce Gateway

Need highly secure forms for data collection pre and post e-commerce transactions. Not-for-profit group wanting to offer online workshop registration, donations and other database integated online member services. Simple, yet secure functionality required. We have all associated XHTML content, mySQL database, merchant account and payment gateway, we only require forms that provide required variables and data management. Potential for additional graphic design and CSS compliant XHTML design as separate project. Forms and back-end programming are three-fold in purpose: 1. Populating fields required by e-commerce gateway. 2. Sending email notification to administrative personnel. 3. Database retention for basic member management such as repeat payments. Prefer smart solutions at higher price (if justified) as opposed to getting it done at least cost.