Hello dshrode,
Thank you for bringing your question to the PayPal community. The PayPal buttons are a great tool for most merchants but their functionality does lack the ability to omit a specific price. If your business model requires custom pricing per customer, it may be best to use invoices or a service like PayPal.Me, which allow your customers to whatever amount they require.
Other than that, you can look into third-party shopping cart integrations that offer this feature as well.
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