if (!$this->getSkipJsReloadPrice()) {
    $extraParams .= ' onchange="opConfig.reloadPrice()"';
}

<catalog_product_view>
    <reference name="product.info.options">
        <action method="setData">
            <name>skip_js_reload_price</name>
            <value>true</value>
        </action>
    </referencen>
</catalog_product_view>

app/design/[your package]/[yourtheme]/template/catalog/product/view/options.phtml

price += parseFloat(config[optionId][element.getValue()]);

price += parseFloat(config[optionId][element.getValue()].price);