Button Add to cart product with price 0

Question

i need in product page add button or links, where when user click on this button, in cart we can send current product but with price = 0

i have button:

<button type="button" title="<?php echo $this->__('Add to Cart') ?>" class="addtocart" onclick="setLocation('<?php echo Mage::getUrl('checkout/cart/add', array('product'=>$_item->getId(),'qty'=>1)) ?>')"/> - button working, but how i can add value from price? 

<button type="button" title="<?php echo $this->__('Add to Cart') ?>" class="addtocart" onclick="setLocation('<?php echo Mage::getUrl('checkout/cart/add', array('product'=>$_item->getId(),'qty'=>1, 'price'=>0)) ?>')"/> - not working

Let me know how i can do better? Thanks

Answer 1

You can make it this way.

Dont change add-to-cart button url, keep it as is.

set proudct price to your desired when it adds to cart on fly. using sales_quote_save_before event.

and set price in your observer.

 $quote = $observer->getEvent()->getData();

 foreach ($quote['data_object']->getAllItems() as $key => $item) {
     if( !$item->getCustomPrice() ){
            $item->setCustomPrice( $customPrice );
            $item->setOriginalCustomPrice( $customPrice );
            $item->save();
     }
 }

Well I have not tested it with 0. But I hope it works.