pearls or shells strung together
賏 centers on the idea of strung-together valuables: pearls or shells threaded in a row, often as a necklace or decorative string.
賏 is formed by doubling 貝 (shell, treasure), visually representing multiple shells or pearls strung together. The exact historical development is uncertain, but the reduplication of 貝 clearly conveys the idea of a string of valuables.
Two 貝 (shells) side by side look like pearls or shells threaded on a string. Picture a necklace made of paired shells: 賏 is that strung-together decoration.
For エイ, imagine an elegant 'A'-shaped necklace of shells: the letter 'A' sounds like エイ, and the strung shells form that shape.