Here are the numbers by country. In case you forgot how we do this, these numbers are for two people, including visa costs and all costs on the ground (and in the air if we took internal flights). Sometimes we also include the cost of a flight into the country if that was the only way to get there.
India: $53 per day. Visas cost $74 each at the embassy in Istanbul. India is one of the cheapest countries we've been to, so staying there for five weeks did wonders for our financial (if not gastrointestinal) health. Hotel rooms ranged from $10-$25 depending on level of comfort (except in Mumbai, where it's hard to find a double for less than $50); restaurant meals could usually be had for a buck or two, and street food for pennies; and train transport in sleeper class cost less than a hotel. Not getting ripped off on cabs and tourist excursions required some negotiating.
Sri Lanka: $80 per day (including flight from Chennai, India, which costs about $120 per ticket; $53 per day without flight). No visa fees. Sri Lanka's hotels and food were a little more expensive than India's, but it made up for it with what is possibly the world's cheapest public transport on a $-per-hour basis. If you plan to visit more than two historic sites in the "Cultural Triangle" area, getting a pass can save you $25 or more.
Malaysia: $47 per day. No visas. Some travelers complain about Malaysia being pricey, but as it turns out, the only traveler item that is really expensive in (Muslim-majority) Malaysia is beer! As long as you don't drink much, the country is terrific value, especially considering how developed it is. Air-con double rooms with shared (but very clean, hot-water) bathrooms cost $10-$15, and delicious, cheap street food abounds. Transport is a little pricier than some Asian countries, but you usually get comfortable, AC buses on smooth roads. We stuck to the peninsula this time and didn't do any fancy tourist excursions, but our memories of our previous trip to Borneo are that prices were very reasonable there, too.
Singapore: $111 per day. No visas. We only spent two days in Singapore, so this is kind of skewed, but it's certainly one of the most developed and expensive countries in Southeast Asia. Most of the cheaper hotels are in the red light district, where we found a decent private room for $35 a night. Public transport, museums, and restaurants are comparable to Western prices, but taxis (which are metered, hallelujah!) and street or food court foods are relatively cheap.
Indonesia: $102 per day. One-month visas on arrival at the airport cost $25 each. Indonesia was surprisingly expensive, though that's largely because we did a lot of pricey activities like SCUBA diving, chartering a boat to Krakatau volcano, and a few other organized tours. No-frills internal flights between the islands were a pretty good deal, usually less than $50 one-way and could be booked just a day or two before. Buses and trains on the ground varied a lot in price and quality. Hotel rooms for $10-$15 could be found, but were usually pretty disgusting; if we wanted cleanliness and AC, we usually had to pay at least $25. Cheap street food could be found in most places, though not so much in touristy Bali, where we usually had to shell out for real restaurants.
Thailand: $83 per day. No visa fees. Considering how many touristy activities we did in Thailand (diving, elephant training camp, etc.), this is a great average. Hotel and transport standards are pretty high, but competition for the tourist buck keeps prices low. Markets selling cheap local food are pretty easy to find, and even fancy restaurants are probably cheaper than the Thai restaurants you find at home. Just try not to get robbed, which could certainly send your costs soaring!
Myanmar: $77 per day. Visas cost $27 each in Bangkok. This average includes flights into and out of Yangon from Bangkok ($130 each roundtrip), which accounted for one-third of our expenditures there. Once you're on the ground, Myanmar (Burma) is super cheap in all categories, though its rough roads, ancient vehicles, and power cuts often made it feel more like traveling in sub-Saharan Africa than Southeast Asia.
Cambodia: $53 per day. Visas cost $20 each at the border. Cambodia is excellent value. $11 a night got us rooms with bathroom, AC, and sat TV in both Siem Riep and Phnom Penn, the two most touristed cities in the country. Markets and restaurants offer cheap food; bus transport and tourist site admissions are pretty reasonable. If we had stayed longer, or ventured out to less touristy places, it probably would have been even cheaper, but even so, Cambodia was one of the cheapest destinations on our trip.
Vietnam: $66 per day. Visas cost $45 each in Phnom Penn, Cambodia. Vietnam's one of those countries that feels more expensive than it is, probably because people are trying to rip you off almost continuously. But we did manage to stay in some pretty nice hotel rooms and eat decent food for not a lot of money. Trains cost more than buses but are much nicer (which isn't the same as saying that they're actually nice!), especially for overnight travel. Halong Bay overnight cruises can be an especially good deal for a decently swanky experience...provided your boat doesn't sink in the night, of course.
Laos: $57 per day. Visas cost $40 each at the border. Laos is pretty poor, so the roads and buses aren't always the nicest, but hotels were quite comfortable, food was inexpensive, activities like kayaking were very reasonable, and prices overall about as cheap as could be.
China: $92 per day. Visas cost $160 each in Vientiane, Laos--the most expensive of our entire trip. (They are about $100 less expensive for non-Americans, though.) Yunnan province, in southwestern China, was incredibly inexpensive; with $10 hotel rooms and cheap bus rides, it cost no more than Laos, where we had just come from. As we moved east and to the bigger cities, things got more expensive, though you could always find cheap and tasty food, even in Beijing. In general, China didn't feel overpriced considering the good quality of rooms, trains, and food that we got, and some tourist attractions, like the Forbidden City, were surprisingly reasonable.
Mongolia: $121 per day. No visas needed for Americans, though most nationalities need one. This number is high because we spent 6 of our 8 days in the country on a private jeep tour of the Gobi. If we'd managed to find a couple of other travelers to share the tour with, costs would have been halved. Otherwise, the country's pretty budget-friendly: In Ulaan Bataar, the capital, a hostel room with breakfast, Internet, and shared bath cost $15; there were expensive restaurants and cheap local-food canteens to choose from; and the 15-hour train from the China border cost around $9 for seats, or $25 for sleeper berths.
So, Asia had a few expensive countries, but was mostly pretty cheap for us. Hope that this post was slightly helpful to you if you're planning to backpack through Asia. If you have any questions, leave a comment and we'll do our best to get back to you!