One of the blogs I follow is an awesome travel group of two humans and two dogs. They traveled in a rig named Skyhorse. If you explore their blog, you will discover why that name is perfect!
Recently they posted one of the most detailed, well-documented set of information I have ever come across on the topic of budgeting. While they are quick to point out that the facts and figures are different for every traveler, the generalizations are the same.
Take a look at their post here https://adventuresinskyhorse.wordpress.com/2015/03/26/budget-recap-breaking-down-2-years-on-the-road/ and consider reading some other pages of their excellent adventure!
BTW- if you are in the market for a unique and tested overland vehicle, Skyhorse is for sale!