Woocommerce modification to variable products functionality

I have products that have a base price, to which options are added. Some options are no extra cost, some are extra cost. The problem with Woocmmerce variable products is that you can't enter a base price for the product, and build upon it. Prices are entered to the variation terms only. That doesn't work for my products. See my CRE Loaded site for an example of how I need a Woocommerce site to work: [login to view URL] Note that there is a base price, and if an option with an added cost is selected, the base price is updated. Notice also that, after all options are selected, 50% of the calculated base price is what needs to be sent to the shopping cart. I've searched available plugins and have found no plugins that can do this. I found discussions where other website owners have been searching for this same type of functionality, but as far as I can tell, none exist. I have no idea what is involved to make this work and am open to bids.