Upgrade existing Volusion online store by writing custom code to add features

I have just built an online store using Volusion, but now need someone who is experienced with Volusion to assist me in upgrading the site. This first project is to write html code to change the way Volusion handles drop-down menu options for a product. As it is currently, "Base Price" is listed for the product, and each time an option is selected, there is an add-on cost, rather than changing the price to the specific product. You can see the current site here: [login to view URL] In the case of my Pet Doors, once the customer selects the size, color, panel height, etc, I want the price to automatically update as each option is selected or removed. Refer to this website as an example of how I want the pricing to work: [login to view URL] I previously built a website for this product using Joomla, and was easily able to customize the product option page so that rather than buying a “base” pet door and then adding on costs as options were selected, the final product cost was shown based on all options considered, which had a specific product code and photo for that specific product. But Volusion does not offer this solution, so we need to work within the Volusion framework make this happen.