What is the accepted amount in shekels in order to fulfill the mitzvah of matanot l’evyonim on Purim?
The accepted amount to actually fulfill the mitzvah is a perutah, which is a very small amount — far less than a shekel.
However, it is preferable to give an amount that would be considered respectable, and enough to give the evyon a measure of joy for Purim. Twenty shekels would probably fulfill this, and some have suggested giving fifty shekels.
Sources: Ritva (Megillah) mentions the sum of a perutah; Rav Elyashiv, and other recent poskim, have been quoted as suggesting a higher sum for fulfilling the mitzvah be’hiddur, and one should preferably give an amount that would cause a degree of joy on the part of the recipient.