Uni Custom Product Options & Calculations is a fully featured plugin that gives a possibility to add any custom options for your WooCommerce products as well as enables custom price calculation based on any maths formula. Moreover, there is a conditional logic for formula – it is possible to create several formulas which will be applied under certain circumstances – user chosen options.

Demo: http://codecanyon.net/item/uni-cpo-woocommerce-options-and-price-calculation-formulas/9333768