It's less about the cost but the time. Starting from scratch it's a couple years before you're good to go to bill a customer task.
Exactly what my wife experienced at her last job. We weren't going to be there long enough for them to justify the time AND expense of going through it all, so she ended up just working for them in an admin staff position. Thing is, had we had the time to stay, there were multiple project leads who wanted her to work for them.