暗恋是所有恋爱中最省钱的
[àn liàn shì suŏ yŏu liàn ài zhōng zuì shĕng qián de]
Meaning that 'secret love is the cheapest of all', implying unrequited love or loving someone quietly does not cost anything tangible because it remains in heart rather than taking real actions such as gifts and dates.