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

比喻東西不值錢因為自己覺得珍貴參見千金

重編國語辭典

東西不好因為自己仍然非常珍視

維基詞典

Entry Composition