Even at night, 1 man with (maybe 3 or) 4 women is probably technically mutar. Similarly for 2 men and 2 women. 3 women with 2 men is pretty good. No less than 3 men with (maybe 1 or 2 or) no less than 3 women is the best.
I don't think sichah im ishah can be called an actual prohibition. See here To what extent can a man talk to women?
Seeing pritzus is also probably technically mutar if you are not trying to. The main problem here is 'if' it brings you to hirhurim ra'im.
Yichud with non Jewish men might also be problematic if they are chashud on shichvas zachar. Also, men can be more dangerous than women if you get in a fight. And if it is only men, then there will probably be more nudity than if it is co-ed.
FYI mixed hostels are generally the cheapest option. And the more beds in the room, the cheaper the beds are.
Also, hostels are for short term stays. Also, hostels generally have automatically locking doors. If you try telling your roommates to leave the door unlocked they might report you to the receptionist.
I once read somewhere, I think towards the end of a Holocaust book, about some men that made aliya and the Zionists only offered them mixed HOUSING. Since they had no other real options they stayed for at least one night.