Add custom text/price to product edit in admin (not custom attribute or editable field)

Question

I have a shop that uses prices excl tax. I want to add the price incl. tax below the price field as text (not as an editable field or an attribute, just an information).

I've already added a new column to the product grid that shows the price incl tax (using a renderer that returns $this->helper('tax')->getPrice($product, $product->getFinalPrice(), true);)

But I just can't figure out how to get this working on the product edit price tab? If I had to add an attribute I think it could be added in the Attributes.php (Mage_Adminhtml_Block_Catalog_Product_Edit_Tab_Attributes), but can I add an info-block/comment/line of text?

It doesn't have to calculate it realtime the price when you enter a price in the price field, just on save/load of the product (with php)?

To sum up, how do i add a custom comment/info text below the price field?

I want to show $this->helper('tax')->getPrice($product, $product->getFinalPrice(), true); in this comment/info text.

Answer 1

Found a way.

Just added the following to Mage_Adminhtml_Block_Catalog_Product_Helper_Form_Price:

... // after: if (Mage::helper('tax')->priceIncludesTax($store)) ...
else if ($this->getId() == 'price'){
        $product = Mage::registry('current_product');
        $price = Mage::helper('tax')->getPrice($product, $product->getFinalPrice(), true);
        $format = Mage::helper('core')->formatPrice($price, false);
        $html.= ' <strong>Price inkl. tax: '.$format.'</strong>';
    }