I have never hobbied in Vegas myself, but from what I've read the general consensus seems to be that both independents and call-out services can be unreliable and misleading (bait & switch) at best and straight rip offs at worst. And don't even bother with the cards handed out on the strip, they're almost always rip offs. Once you start heading into the higher price range ladies ($600 US/hr+) things get better, but not everyone is looking to spend that much. The best success stories I've read usually involve meeting working girls at the hotel bars. Apparently, even if you can't tell for sure if a lady is "on the clock", if you sit by yourself at the bar for a few minutes you will usually be outright propositioned. Prices and times can be somewhat negotiable, too. Again, this is all 2nd hand...
If bar dates aren't your thing, TER has lots of Vegas reviews and you might be able to find someone reliable and in your price range if you search enough.
