It totally depends what you're after and what your expectations are. PR gets very difficult if it's purely results driven, on some accounts i would have been ecstatic at such a deal, but mortified at others. It does depend on the market, the passion for a product at the time and the newsworthyness of it.
To give you an idea, an old company of mine charged a very well known Scooter company 5K a month. We gave Jamie Oliver one, and the company sold out for the next 2 summers. We got paid no more than the agreed amount.
However some fees can be as minimal as 600 a month, for a press release, follow up calls and a newsletter.
What are you after?