In my store (Fry's foods), they had two terminals (Western Union & Checkfreepay) for bill pay. In checkfreepay they could not locate Mastercard, Visa or Discover to pay the bill. In WU they were able to locate and I had to fill a form to know the convenience fee and for $500 bill it came out to be $16. I passed it.

I did visit Walmart yday and paid a mastercard bill for $1.88 convenience fee for $2000 (4 swipes).