In the Rama on SA OC Siman 605, we find the custom of "Kaparos" that many do Erev Yom Kippur. Of those who perform this custom a chicken is used. However many also use money (i.e. instead of waving a chicken over their head they wave money and then give this money to Tzedeka. The wording of the prayer that is said is changed appropriately.)
What is the earliest source for the custom to use money instead of a chicken? The earliest I found so far is the Chai Adam in Klal 144 Sif 4. Although I want to know if there is a source earlier then this.