One of the things to keep in mind is that bench services is able to be set prices by having strict caps and contract limits and enormous margins so that they can absorb a lot of mistakes. Normally they rely on being a loss leader for sales, as well. Look at GeekSquad or Staples, their bench services are only there to improve sales. You need the sales to make it make sense.
IT departments, even internal ones with crazy amount of control, can't have set prices. There are just so many variables. You can work to be predictable, but getting a set price for internal IT is really not something that you can do.