I think it is very cheap compared to Hong Kong. I think you still got some special rate to London. From London you can take either Wizz Air or Ryanair, which are low cost flights. I flew with 20$ that distance. There are good hostel like that one mentioned or you can try couchsurfing. A lot of people will welcome you, just check the history on the profile. In 10 days you can make also a Transylvania tour.