Look at the Inflation Calculator app. If you put in 1940 and $50, today's value is about $115. If it was earlier, say, during the Depression, it obviously would have been worth more. No, it doesn't guarantee anything, but from the bribers' point of view, it probably didn't break the bank and nothing ventured, nothing gained.
So, honestly, you don't think people ever tried to buy votes? Maybe Tammany Hall?