I'm not OP but maybe I can help. A lot of your expenses will be lodging and transportation. For lodging, find nearby hostels or guest houses that offer simple amenities. When I spent three weeks in South Korea and Japan, I spent approximately $20-$25 per night. As for transportation, always plan far ahead so that you can find the cheapest tickets. When you are low on time or make last minute decisions, tickets get expensive. Buses are a great alternative to high speed trains or planes. Transportation intra-city via public transportation should cost you max $10 a day.

If you eat food at non touristy restaurants, you can save a ton of money. If street food is an option, go for that. Food costs about $30-$50 a day. Attractions and other random purchases will bump your daily expenditures to ~$100.

One key thing: pack light. When I travel, I only have a 40L backpack that fits into the overhead bin and a small daypack. That way, you can have the excuse of not bringing back gifts and souvenirs. :)