敝帚千金

zhǒuqiānjīn
  1. lit. my worn-out broom, a thousand in gold (idiom); fig. sentimental value
  2. I wouldn't be parted with it for anything.

CEDICT

  1. (figurative) to cherish something of little value simply because it is one's own
  2. to cherish something of little value simply because it is one's own

Wiktionary

比喻东西不值钱因为自己觉得珍贵参见千金

重編國語辭典

东西不好因为自己仍然非常珍视

維基詞典

Entry Composition