(a) A Perutah is worth about 1 penny, based on the assumption that it is 1/40th of the price of one gram of silver (see Background to Kidushin 2:2a for a general (if not particularly accurate) calculation).

(b) Rav Yisroel Pesach Feinhandler (author of Sheilos u'Teshuvos Avnei Yashpeh) replies that "since the Igros Moshe wrote about cigarettes 'Shomer Pesa'im Hash-m,' there is an obligation to return them to the owner." It therefore follows that one does not return something which is certainly dangerous or forbidden, because of the rule of "Lifnei Iver Lo Siten Michshol." It also follows, in your specific example of cigarettes, that according to the Poskim who rule that cigarettes do constitute a clear Sakanah (a view which some disciples of his assert that even Rav Moshe Feinstein zt'l agreed with years after he wrote the Teshuvah), one should not return them.

Also, when determining whether one should return the lost object, one should try to discern whether the one who lost the dangerous object plans to use it himself, or plans to sell it (such as to Nochrim).

(c) Rav Feinhandler replies: "A person does not have to lose money to fulfill the Mitzvah, and handling anything illegal could cause a loss of money, and thus one is Patur from returning it. Something Asur cannot be returned, as it would constitute 'Lifnei Iver.'" Again, when determining whether one should return the lost object, one should try to discern whether the one who lost the Asur object plans to use it in a forbidden way, or he plans to use it in a permissible way.