rate of inflation is about 3-5% a year.  Now add that to the cost of hotel, site membership, traveling expense, clothing (everyone wants a lady to look sexy), $400 seems to be the average for the Bay.  Well reviewed ladies will go over that price.  Although, if you schedule multi hours, you usually get a discount.

I consider  
100 to 250 cheap
300 to 500 mid range  
600 and up is high end

Maybe your just looking in the wrong category for your spending limit

As of now, many of the ladies who are attractive and GFE are in the 350/400 price range. A relatively new lady might be 300. That's not a major price increase. The Bay Area is too competitive to have a major price increase.

The 500+ ladies are often part timers who don't work that often. Many of the ones at 1K are porn stars or centerfolds. They usually work through an agency. Agency girls are giving 50% to madams.  

If you look at the various advertising sites, you should find quality GFE ladies in the price range I mentioned above.

Don't forget hotel prices have definitely increased in the bay area and that in itself will raise prices.  If you look a bit closer the same lady usually can be found for less in the Sacramento area verse the SF area.