What countries are less or more expensive has come up a few times on different threads. But usually as off topic. But I found the topic curious and did some digging. But rather than trash those thereads wiht off topic info I put some information here.
This survey https://theworldtravelindex.com/en/countries/low-cost-index was the easiest to decipher but I could find nothing about how they derived their results. I looked at a few other surveys on the same subject and they all track pretty much, but not exactly, the same. I call this sort of thing, "something to keep in mind when planning but not necessarily fact". The lower the ranking the cheaper to visit. Remember "for a trip" which isnt necessarily exactly the same as the cost of living in a location.
Ranked from 1 to 48 in the world were Ukraine, (ranked 11th in the world), Azerbaijan (arguably in Europe), Georgia (arguably in Europe), Moldova, North Macedonia, Bosnia & Herzegovina, Armenia (not really in Europe), Bulgaria (ranked 48th)
Ranked from 49 to 97 in the world, Serbia (ranked 51st), Romania, Poland (ranked 61st in the world), Montenegro (ranked 65th, the cheapest country using the Euro), Albania, Hungary (83rd), Slovakia (ranked 91st it’s the cheapest country in the Eurozone), Latavia, Portugal (Cheapest country outside of the old Soviet Bloc at 94th in the world)
Ranked from 98 to 146 in the world, Lithuania (ranked 103rd), Slovenia, Spain (ranked 112th in the world), Czech Republic, Croatia, Estonia (ranked 133rd and the most expensive of the old Soviet Bloc countries), Malta Greece, Andorra (ranked 141st)
Ranked 147 to 193 in the world, Italy (ranked 150th), San Marino, UK, France, Germany, Belgium, Austria (171st), Netherlands, Ireland, Finland (ranked 181st, the most expensive country on the Euro), Sweeden, Norway, Denmark, Iceland, Monaco, Switzerland (rated 193rd and the most expensive place to visit in the world).