Every year the Post Office do a survey about costs in 42 destinations worldwide. For the second year, Bulgaria (in particular Sunny Beach) was the cheapest. Marmaris in Turkey and the Algarve were next cheapest.
For long haul destinations – Cape Town, Tokyo (surprised me) and Kenya were the best value. More details here https://www.postoffice.co.uk/travel-money/holiday-costs-barometer
Let me know where you want to travel to and I’ll give you an idea on costs to expect while there.