Time is the most important consideration before money, do you have it now and can visit 150 countries in one time frame or spread your travel over the rest of you life? Lets have some fun, 1 month in each country on average is 12.5 years of non stop travel. The problem your having to do it backpacking style and cheaply means you need to SLOW down and take more time to do it cheaply and acquire money along the way. I saw 100 countries from 1979 to 2002 =23 years at $100,000 Australian dollars. Most of my travel was at around $20 a day. I was working at home saving and took many 4 to 12 month trips.
Sadly some of the most beautiful countries are the most expensive. Norway is a must see, you may be so clever to get a $30 budget flight from another country to Oslo but shock sets in when you get the bus from the airport to the city at $30, so you need to be much more resourceful in the rich countries to travel cheap. Travel will not be fun unless you love a challenge, how to avoid that $30 bus fare, would you ask people at the baggage carousel for a lift into oslo, would you hitchhike or just walk. Maybe you arranged your new found couch surfing host to pick you up at the airport for free. To learn these budget travel skills takes time , you will make costly mistakes along the way in order to learn the ropes.
Money, in our 150 countries over 12.5 years @ $20 a day = $91,250.
This is not realistic as you cant normally live less than the locals
In Norway they earn $100,000 a year or $274 a day on average.
Your options in rich countries are very limited, avoid them, minimise your time there or work for your keep. Generally your best off to work hard at home and save all you can and minimise your time in rich countries.
In Cambodia they earn $1500 a year or $4.10 a day on average.
It is possible to get $1 very basic dorm bed, eat well for $2 a day but that cultural attraction you came to see, the Ankarwatt temples will cost $30 a day to enter. Dont worry it will average out to under $20 a day.
There is 192 countries in the world, you want to see 150 so you dump 42 countries. You need to choose carefully depending on your funds.
your daily budget for world region
Asia/Africa $20 a day ( the richer of these countries like japan consider western )
south america $20 to $50 a day
north america $50 to 100 a day
eastern europe $30 up
central europe $40 up
western europe $60 to $100 up
Assume your a hard nosed experienced street smart budget traveler who does not want to work to see the 150 countries. Stay in the cheapest dorm or room, eat local food and use local transport and fly only on promotions on budget airlines. spend a month in each country on average.
Choosing the 150 countries
Asia /africa 80 $49k
south america 10 $9k
north america 20 $43k
eastern europe 5 $5k
central europe 10 $12k
western europe 25 $53k
Total 171,000 usd over 12.5 years is realistic but not easy for the following reasons.
Many countries will give you expensive and logistical visa nightmares.
There will be expensive flights that can't be avoided.
You will have to break the trip up into several trips, going back home will cost you dearly, from there you have to start out again, so airfares will be much more than you thought. Also if only one month in a country, you will be on the move to see several cities, so your transport cost's will be much higher than you expected.
Is it worth it? Being away from friends and family who will never understand why you did it or be able to comprehend your excitement and your stories, they are simply not interested as they can't relate.
What about your carrier, you wont have one at the end of your travels, you will have to be a entrepreneur or create your own income as you will be unemployable. How many investment properties could you have bought in 12 years??? There is a real price to pay and your will be a different person as to when you started out.
You need to start your quest as young as possible as you have the energy then and are willing to suffer more, at age 60 you may not want to sleep under a bridge or on a airport floor to save money.
What is you motivation? Guinness world record entry? It would be a very expensive exercise just to say you did it in x days. Soaking up culture happens when you live in a place for at least a month, and more so in a year. A year in each country starting at age 20 +192 means your 212 years old.
Blasting around the world in 1 year is less than 2 days per country.
So you really need to plan what is best for you.
Don't let any of the above stop your dream, plan to the best of your ability, do all your worry before you leave, hit the go button, the travel gods will take care of you after that point.