Hi OP.
Some thoughts.
Firstly I'd advise against having a concrete plan (or spending money) until after you move in.
I think it's often best to move into a house and see how it works for your family life before making any firm choices - this is especially important if your budget it tight.
Secondly think about what your sons really need.
Obviously the ideal would be their own rooms, but with the space and limited budget I can't see how that's achievable.
That said if my teen DS is anything to go by a bed isn't his his rooms focal point.
What he values is his desk and space/privacy for gaming/contacting his friends online.
With this in mind I'd be temped as pp's have suggested to divide the room using bookcases between the windows.
Make sure there is room for a bed (plus clothes storage) plus a desk in one section (you might need to make this section a bit bigger than the other).
Then what I'd do is look to put a desk in the dining room (you can get nice fold away versions).
This way each child gets their own "gaming" space in the evenings (and you get the lounge).
Realistically I think they would value gaming privacy over bed privacy - but ask them what they think.