$100 a day!? That's not living simply - that's staying in hotels and eating in restaurants. I'm an active CouchSurfing host and I've met many travellers who get by on $100 per month. And that's in Europe. You can stretch that out for 3 months in lots of parts of Africa or SE Asia.
CouchSurfing and equivalents can drastically cut your accommodation expenses. Hitch-hiking or cycling give you free travel. Even travelling by bus can be remarkably cheap in most countries if you go the slow way (which also lets you see much more of the country that just the capital) - you can often go 50-100km for a couple of euros. Your primary cost is food, and if you've learned to cook even a few basic meals, you can easily get by on a couple of euros a day.
CouchSurfing and equivalents can drastically cut your accommodation expenses. Hitch-hiking or cycling give you free travel. Even travelling by bus can be remarkably cheap in most countries if you go the slow way (which also lets you see much more of the country that just the capital) - you can often go 50-100km for a couple of euros. Your primary cost is food, and if you've learned to cook even a few basic meals, you can easily get by on a couple of euros a day.