With this type of adventure, you can get your cost down to maybe 5-10k/year if you travel light (bicycle, motorbike) and camp out a lot. Source: Quit my job and rode a motorbike from Central Europe to Mongolia. One of the best decisions I've ever made.
On a only slightly related note: there's a guy who drove across a lot of Asia and Europe on a C90. He filmed some of it and cut it togheter. Here's an example: https://www.youtube.com/watch?v=_2LEgowbzSc
KLR 650, it is pretty heavy in the mud but easy to work on.
Many adventure bikers start taking light, modern, powerful fuel injected bikes for long range trips now, like the WR250 and the KTM 690 Enduro.
I saw some guys struggling hard with GS1200s in sand and mud. If you know you're going to drop the bike a lot, it's probably worth going for a lighter option.
