To the best of my recollection it’s from The Grapes of Wrath and was spoken by either Tom Joad or Jim Casy, but I don’t have the book at hand and Google has failed, as has Wikipedia.
Does this line ring a bell with anyone?
SS
on edit; On reflection, I think the actual wording may have been “A man’s just as free as he’s got jack to pay for it”
Ah…what a difference an apostrophe makes eh? And I see now 'twas neither Tom nor the preacher that said it, but the un-named proprieter of a roadside garage that was engaging in a bit of profiteering.