This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 賷 is uncertain. It visually contains 貝 (shell/money) at the bottom, suggesting a possible connection to value or goods, but the upper component's origin is unclear.
The bottom 貝 hints at money or value, but the complex upper part makes the overall meaning unclear. Think of it as a mysterious treasure chest whose contents are unknown.
For セイ, imagine saying 'say' to this mysterious kanji, as if asking it to reveal its meaning: say -> セイ.