Unfortunately, your post doesn't make sense. If you need to port websites over to I would imagine there is no easy way to get that accomplished. There are so many variables that come into play even without entertaining the idea of modules that might be installed on your Joomla instances. You are probably better off rebuilding these websites then transferring them.
To answer your questions:
Do you have any idea how can I reduce the cost of human costs of running lots of Joomla sites?
If it is management you are after I would hire somebody to update the content on your sites instead of doing the work yourself.
Do you experienced any multi-site Joomla good solution?
Never, thus far. I don't think Joomla is a good solution but I haven't invested much of my time in it really.