I don’t think that it was the monetary value that triggered the massive search- since as ZD said, the search probably cost way more than a new pair.
Nor what is it for the sentimental value, or the fact that they may have historical significance.
It is the fact that tefillin are tashmishei kedusha and should not be in a garbage dump. Even if they were ruined.
In the zechus of all that was done to preserve kavod shem shamayim and kedusha, may those involved in the search be blessed!