YITH WooCommerce Name Your Price allows your users to buy products of your shop at the price that they choose, if that price matches your settings.
You will only need to install and activate both plugins, to make them work.
Your users first set their own price for the product and then add this to the quote.
The admin receives the quote request as usual. He sees the price entered by the user, can confirm or edit the price and send his/her own offer.
Check the complete documentation on how to set up YITH WooCommerce Name Your Price here.