Sidi looks at her potential bride-price as a monetary expression of her value as a person. She has a very high opinion of herself and fully expects that any bride-price will reflect her exaggerated self-regard. If Lakunle wants to make her his bride, then, he's going to have to put his money where his mouth is.
But Lakunle won't; he thinks he's being a modern man by refusing to go along with what he regards as a degrading, antiquated custom. His value system is clearly incompatible with Sidi's; she still cleaves to the old traditions, which she believes give women like her a sense of security. These customs may not benefit every woman, but for shallow, superficial women like Sidi for whom appearance and status are everything, they seem to be just the ticket.