You really need to check the provider's ad or web site to understand her pricing and if there are add-on services. But could also be a typo when someone put the price in. Depending on the pool you want to play in 350 is pretty average pricing but you can definitely find some where the average hour is less, and definitely find some where it is substantially higher.

 
So I'm not sure if you're asking about over all trends or a specific provider and differences in prices various clients paid.

What area are you from? And what site is the girls ad on? In my area 200-300 for 60 minutes is very common for girls who work off ListCrawler but 500-600 is more average on sites like Tryst and if your looking for the higher end it could be 1000-2000 the hour. There are girls for every price range so just go with what you prefer, but keep in mind paying more does not mean the service is better, in my experience I'd go off reviews only, I have seen girls for 100 that go above and beyond vs 4000 at someone I didn't have a great time with.