How to divide a living room so that part of it can also be a bedroom?

I’m living in a smallish two bedroom apartment with two other friends this summer. None of us particularly want to share a room, so we’re converting part of the living room into third bedroom space and alternating who lives in it month by month. Ideally we’d like to have a living room space, albeit small, beside the bedroom, so that we can still sit on couches and stuff without disturbing our roommate too much.

The problem is that the living room is very large and doesn’t have a doorway. The other problem is we’re too broke to buy expensive room dividers to separate out a space. The place is a rental, so we can’t really attach a permanent fixture to the room like a curtain rod or anything.
Here is the floor plan. Any suggestions for cheap ways to create temporary room dividers?