I regularly do multilayer boards at home. Once you have a through plaiting setup, this is relatively simple. As a rough estimation you can say that you need a total processing time of one hour per layer. So, a 4 layer takes 4 hours and so on.
Obviousely a through plating setup and a CNC drilling machine cost some money, so for the average hobbyist this is not an option. I made my own througplating machine and hence could save a lot of money I otherwise would have to spend to buy one. Smaller CNC drills are relatively cheap these days so at least for me it was worth the investment.
Personally I think making your own boards is having a lot of advantages apart from the prize argument only. But while we are talking about prices, there comes a break even point with increased complexity in that prototyping prices for multilayer boards (especially those >6 layers) seem to rise exponentially. Another point is the fact that even when I do my boards myself many kind of work can be done unatended.
Elsewhere in this thread you mention also the time one has to wait up until externally made boards arrive. This is a very valid argument and the waiting time significantly varies depending on where you live. At the risk of outin myself of not being perfect, this becomes a real issue if you discover some sort of error or find some important optimisation (i.e. because of space constraints etc.) once the board arrives.
Just my 2¢ of course.
Markus