How to change price, the price calculation in cart through custom module Magento 2?

Question

Here in my custom module:

This product with 50 quantities price is 6,000

But when I add to cart this multiplies

So how I can fix this?

Can I use observer to change this or are there any other best way?
Thanks

 if ($quoteId != 0 && ($priceOne!=$item->getCustomPrice() || $quoteQty!=$item->getQty())) {
                $flag = 1;
                $item->setCustomPrice($priceOne);
                $item->setOriginalCustomPrice($priceOne);
                $item->setQty($quoteQty);
                //$item->setRowTotal($priceOne * $quoteQty);
                $item->setRowTotal($priceOne * 1);
                $item->getProduct()->setIsSuperMode(true);
                if ($helper->checkAndUpdateForDiscount($item)) {
                    $item->setNoDiscount(1);
                } else {
                    $item->setNoDiscount(0);
                }
                $item->save();
                $this->_messageManager->addNotice(
                    __(
                        "You can't edit quote items"
                    )
                );
            }
        }
    }

Answer 1

I still think you probably want to set price to $120 and then control available qty's via the frontend. Then you might want to enforce qty's allowed in cart via a quote observer/interceptor.

To provide you an answer to the question of how to manipulate price for products in the cart a method I've used before is to observe the sales_quote_product_add_after event. Below is a basic idea of the concept:

Company/Module/etc/events.xml

<event name="sales_quote_product_add_after">
    <observer name="company_module_quote_product_add_after"
              instance="Company/Module/Observer/QuoteProductAddAfterObserver" />
</event>

Company/Module/Observer/QuoteProductAddAfterObserver.php

...
class QuoteProductAddAfterObserver implements ObserverInterface
{
...
    public function execute(\Magento\Framework\Event\Observer $observer)
    {
        $items = $observer->getEvent()->getData('items');
        foreach ($items as $quoteItem) {
           //...custom logic to items in cart...
        }
    }
}