Allow Customer To Enter Amount

The plugin simply takes what’s in your cart and passes it to PayPal for processing. You would need to customize your site to let people enter their own amount for a product they’re adding to the cart.

This can be done with WooCommerce extensions. WooThemes themselves make one called “Name Your Price” that would do that for you. Then people could fill in whatever price they want on an item you have setup, and then they could checkout accordingly.