I have lived in many countries thanks to my freelance career. I will give you a comparison of cities to choose from.
Istanbul, Turkey:
This will be your cheapest Europe option. People live on literal 300$ here. The food is amazing and cheap, the people treat tourists like kings (be careful for getting overpriced or scammed though), plenty of sights and nightlife, and you are surrounded by water (makes for a nice view while you are riding around)
The cons are that there is high political repression (you can't speak about the govt) and the internet is censored and slow, you need VPN for anything sexual or political.
Bucharest, Romania:
Where I currently live. I live in a 300$/mo studio and my food utilities etc all comes down to 600$ per month max. I have 400$ left for hookers, adding to my travel budget, or medical stuff etc. It's a very liberal country and the people are very chill, lots of natural sights to see and awesome nightlife. The cons are that it's ugly (commie blocs everywhere) and can get dangerous in certain areas at night.
Warsaw, Poland:
I did not really enjoy this city, the people are cold and nationalistic, it was cold all the time and the public transport has very few English translations, but its cheap and has good nightlife.
Berlin, Germany:
Very difficult to survive with 1k a month here especially if you are not single. Has awesome nightlife and food though, people from almost every country in the world and its very diverse and free.
Manila, Philippines:
This was probably the most fun city I visited, great nightlife and beaches, you get your bang for buck for apartments and condos, and also the people are very friendly and helpful to tourists. English speaking rate is very high and it helps being more comfortable there. The crime rate is very high though so if safety is a consideration I would avoid (I have an adventurer personality, you may not, it's fine)