Shaikh Ibn Uthaymeen was asked the following question:
What is the highest amount of lost money that is allowed to be picked up in this time period?
Do you mean that which will belong to him by picking it up or the amount that is allowed to be announced that it is lost?
That will belong to him by picking it up
That is because there is difference between them. So that which is allowed to announce as lost is any lost item even if it reaches millions. However, that which will belong to the one who picks it up differs according to the difference in conditions and people. In the past, one dirham was expensive with the people; it was followed with concern. In our time, it is possible ten riyals is not important. If a person lost ten dirhams, he would not search after it except if it was in a close place. However, when dirhams became plentiful in the hands of the people, liquid, as they say, if a person lost fifty riyal, he would not be concerned. However, now greed for dirhams has emerged. So sometimes we say thirty riyal is followed after with keenness amongst the people, so it must be announced [as lost]
Faisal Ibn Abdul Qaadir Ibn Hassan