I suspect I may be able to speak to this with a little more authority than most. I have owned my mog for 7 years now. As far as a price goes, it completely depends on condition, with running 404's going for 4-15K, 406 going for 8-40k, 416 for 12-50k, and 1300 for 18-60k, etc, etc. All of them can come with PTO. All of them except the 404 can come with hydraulics, dump beds, you name it.
The 404 is a different animal from the rest. If you haven't driven a mog, I suggest at least driving one before buying. Like others have mentioned, they are definitely not like a heavy US truck or even built buggy.
While surplus parts are common for 404's, you should be warned that parts for the rest, while available, are expensive. The good news is that they are very reliable when they have been maintained. The main thing to check on used ones is that the tranny and portal boxes are in good condition - lubed up and no water.
I think they are cool, but I am very biased
Feel free to contact me on or off the board with any questions or tell me a little about the mog for guidance on price.