How to edit the cost of the order by the buyer?

Question

WordPress

Tell me if there is a solution, is it necessary for the client, when placing an order, to be able to edit the cost and already the quantity of goods is pulled up from the cost?

For example:
Selling cakes, when placing an order, the price for 3 kg is 3000R.
The client changes the price by 3500r and the quantity of goods is increased to 3.5 pcs.