I booked a Budget car through Expedia.com (USA), in France. Between when I booked it and when I picked it up, plans had changed and I would have to return the car a few hours late.
I understand that can cost me an extra day's rental, no problem. When I mentioned this to the guy in France, he said he could change the reservation if I wanted, but now it would be the French rate and the extra day would cost me the equivalent of 5 days rental! I said no thanks.

Worried about what they would charge me I eventually phoned Budget France and they basically said they could charge whatever they want for the extra day but couldn't tell me exactly how much because there was no manager present.

Is it really the case that rental agencies can charge anything they want if you bring back a car a few hours late? I'm renting for 13 days and paying about 23 euros a day. They wanted 150 euros extra to change it to one more day. I intend to just bring it back late and see what happens. If they overcharge me I'll take it up with Budget (USA) or Expedia.

Any thoughts, experiences, advice?

Thanks.