Magento 2 services handle custom option pricing by storing a price and a price type for each option value. Magento 2 services support two price types: fixed and percentage. Developers set price and price_type when adding options via service contracts or API. During cart calculation, Magento applies fixed amounts directly and computes percent values from the product base price. To change the base for percent, add a plugin or observer. Use service contracts to validate and save option data. Test across store scopes, currencies and tax settings.