2 weeks in Central/Eastern Europe in June

I’ve been sort of forced into taking a 2 week last minute annual leave in June – effectively have 15 – 16 days in total to play with.

I’m from the UK but never really done central or Eastern Europe. I’ve backpacked around most of Western Europe, SE Asia and Africa a few years back in my late teens and early twenties and I’m 28 now.

I’ve been thinking of some places I want to visit based on recommendations and things I want to do a bit of in this period:

Budapest
Montenegro
Serbia/Albania
Slovenia
Turkey

I want to split time equally between:

City and culture
Bars and nightlife
Mountains and hiking
Beach/lake chilling

I’m thinking in reality I only have time to 3 cities/locations properly in this period .

Happy to stay in hostels or hotels depending on place and ideally spending as little as possible on accommodation… Backpacker/party hostels are great as long as they have good reviews!

I would be flying out/into Heathrow or Gatwick. Rest of trip between or within countries can be bus, train or flights.

Budget: £1700

Does anyone have any similar trips or experience on planning a little trip like this?

Thanks in advance!

2 weeks in Central/Eastern Europe in June