The downside of winter is that it is high season in SEA and cost will be higher. In summer you can comfortable live for $20-25/day (hotel/food/scooter + some incidentals) if you have limited needs in a place like Siem Reap.
South Asia can be done in winter for less. Nepal e.g. is cheap - with monthly rentals for about $200. A maid/cook for about $100 and food cost about $300/month.
If you drink the cost goes up quickly - except for Vietnam where a draft beer is about $0.20 (or less) but the general cost of living is higher than surrounding countries.
Visa cost is also worth considering as these can add up if you want to stay over 30 days.