Returning for Free
If one sees the lost item of a Jew that he is chayav to return, he must return it free of charge (שו''ע חו''מ סי' רס''ה ס''א ). After he picks it up to return it to its owner, he must do everything he can to return it, even if it is worth very little.
L’chatchila, the finder should not take payment for returning it. This is like all other mitzvos, which one should do free of charge (שיטמ''ק ב''מ דף ל''א ע''ב ). Nevertheless, if the owner of the item urges him to take money for returning it, he may take the money (תשובות והנהגות ח''ג סי' תס''ג ).
Monetary Expense
Will cause a loss. One is not chayav to spend money for hashovas aveida. Thus, if one will suffer financial loss by returning an item, he is patur from returning it (ב''י חו''מ סי' תכ''ו, סמ''ע שם סק''א ). Even if it will merely cause him not to profit, he is patur (שו''ע הרב שם ). However, if he is sure the owner will compensate him for his costs, he must spend the money (ב''י שם הרא''ש ).
Lower wages. If taking care of hashovas aveida will cause one to be late to work and receive lower wages or late to kollel and receive less money for shemiras sedarim, he is also patur from returning the item, as reduced wages is considered a loss (משמעות מ''ב סי' תקל''ט סקכ''ב וכ''ג ).
Bitul Torah. Even if doing hashovas aveida will take away from one’s learning somewhat, he must return the item, as the purpose of learning is to fulfill mitzvos. This is not comparable to financial loss (הגריש''א, במשפט האבידה סי' רס''ה שע''צ סק''ט ). Also, he himself would have bitul Torah for his own loss (הגר''מ פיינשטיין קו' השבת אבידה ).
