Had my old Weimaraner of 13 years put down in March last year. It was as simple as a call to the vets, they sent someone out and then the bill was sent in the mail about a week later. I am not sure if this is normal practice but I would be thinking about my pet more than the money now at any rate.
500 notes seems bloody extortionate though, making that much profit on something any caring owner would ask for, if I remember correctly it was around 230 to have our dog put down, and even then I think that is too much, but it was necessary.
I would be suprised if they asked for it at the time, considering the loss of a pet is a very significant thing to pet owners.
The vets we use are very good though, my family has used them for a very long time and we have always managed to get a hold of a vet at short notice. If the pet they are coming to see is old/very ill and would be placed under uncessary stress by taking them to the vets, they don't charge for a call out either.