'...A Measure of Wheat for a Penny...'
"Weighing the bread is a sign of a curse, according to Leviticus 26:26 'They shall dole out your bread by weight; you will eat, but you will not be satisfied.'"
(Commentary to the New Testament, Yechiel Lichtenstein as quoted in Jewish New Testament Commentary by David Stern)
A penny of silver, which one of gold exceeded twenty-four times; for A penny of gold is worth five-and-twenty of silver. The canons of the Hebrews concerning hiring of labourers distinguish, as reason requires, between being hired by the day, and being hired (only) for some hours: which may be observed also in this parable: for in the morning they are hired for all the day, and for a penny, but afterward for certain hours; and have a part of a penny allotted them, in proportion to the time they wrought.
Commentary on Matthew 20:2
(A Commentary on the New Testament from the Talmud and Hebraica, John Lightfoot)