1

Depends on so many things.........

Where you want to go (exactly)...how you want to live.....what you eat...which 'activities'you do....how fast you move from one place to another.......how you travel etc etc.

There are people who plan to spend, on the itineraries we get all the time on here......anything from a few thousand dollars(planning to hitch,sleep rough,couchsurf everywhere) to $50,000 for a year's travel!

2

Take Africa,for example...you could easily spend 10 times more in (say)Gabon than in Egypt.

But you could also spend more in Egypt..if you stay in 5 star hotels,eat in restaurants,do loads of organised tours and activities.

3

I guess it wouldn't be slumming it, but it would be using budget accommodation wherever possible. A lot of it would be done by train, with the odd flight here and there if we needed to traverse overly large distances. Activities would generally be sightseeing, with only the odd paid excursion per place we visited.

I imagine Central and South East Asia would take up a fair bit of our time, and I'd love to visit the likes of Borneo for the wildlife, ending the trip in Australia and New Zealand. Africa would be cool, but maybe not viable in terms of cost to combine it with Asia.

4

Africa would be cool, but maybe not viable in terms of cost to combine it with Asia.

Depending on where in Africa you are, flights from Africa to Asia aren't that expensive (take a look at airlines like Ethiopian airlines or Kenya Airways although, sometimes airlines of the Middle East like Emirates or Qatar Airways have some good fares).
If you want to visit India before arriving to South East Asia, you can look either for direct flights (or connecting flights with a change of planes with a major airline) or for two low cost flights (e.g.: FlyDubai or Air Arabia): one from an airport in East Africa served by any of these two low cost airlines to the UAE and another one from the UAE to India with the same airlines I quoted.
As you talked about Central Asia, be aware that Air Arabia has flights to Almaty and that FlyDubai has flights to Bishkek and Ashgabat.
If you plan to use the Trans-Siberian, this web will provide you an estimate of the cost of transport for that leg of your trip.

P.S.: I think if you cross-post your thread in the Gap Year & Round the World Travel, you can get more answers to your questions.

5

how much does it cost you to live at home
how much do your local holidays cost
if you have an expensive house or rent then your accommodation costs will be higher than staying in a dirty backpackers hostel
if you go to expensive restaurants your meal costs will be higher than eating street food
if you go to an expensive retreat for holidays at home will you be expecting that all the time you are away
work out a realistic daily cost of living at home then round it up then add 10% then round it up again
probably wont be much different on average with some countries more and some less
home costs should include everything like movies beer opera birthday presents gas electricity car as when you are away there is a lot more to do than eat sleep and transport and if you haven't budgeted properly something good has to be given up

6

Would it be dangerous if you were slumming it to sleep in run-down hostels/rooms? How about sleeping in tents on the outskirts? Is this too dangerous?