They don't buy $1000 of bonds from you for $1000 dollars. The whole point is to push yields down. When yields go down, prices go up. So they are buying what was

They don't buy $1000 of bonds from you for $1000 dollars. The whole point is to push yields down. When yields go down, prices go up. So they are buying what was $1000 worth of bonds for more than $1000.