I've heard some south east asian countries are cheap. The Philippines stands out to me since I've heard online you can get a lot with a pretty small amount of cash.
It all depends where you are coming from I guess, I found NZ and Australia really cheap when there because of the exchange rate of almost $2 to the pound. Flights were a bit more however If you use sites like kayak or skyscanner and are flexible when you go/ where you go via you can get it pretty cheap. I went to NZ via Kuala Lumpur with an 18 hour lay over and it saved me £150, I then paid £15 for a container hotel overnight and waas sorted.
Thailand though is cheap as chips and absolutely fantastic if you avoid some of the party places like Koh Samui,. I spent a lot of time on Koh Tao for scuba diving and little hut, food etc all cheap as anything.