"Pennies on the dollar" means a small fraction of the original value. The example here is that if you owed me $1,000, and I was unable to collect that money from you, a collection agency could buy your debt from me. Since that debt has no value to me, I might sell it to the agency for $50 (5 pennies on the dollar). This is $50 more than I thought I'd get. The agency would then employ various methods to collect the money (the original $1,000) from you.