It totally depends on which part of Europe you wish to travel. An average cost of med-range trip in the western parts is easily EUR 100/person/day. The same comes down to EUR 70/person/day. This includes stay, transport, activities & food. The 2 big cost buckets are - accommodation & transport - this is where you can spend a lot but if managed well can considerably get your budget down. Read more specific countries on my blog:https://khyatimaloo.com/
Depends on number of days and countries you are planning, it varies a lot. But there are budget tips for Europe specifically, you can refer my blog on Europe budget in tripoto