Back page has changed its pricing rules, and no longer allows advertisers to publish prices for anything less than an hour.  No more half hour or 15 minute prices.  For now, some of the posts have prices clearly listed for an hour or more, and then somewhere in the ad is just another unexplained number, with no indication what it is for. Its pretty easy to figure out that that undefined number is for shorter sessions.  

The talk is that BP is trying to avoid some of the troubles that Craigslist went through.  Though, I cannot see how only targeting "short session" prices accomplishes much of anything.