I just went through this with our bedroom.
I went to IKEA and found a rail system that worked well for us. They have a big range of curtains, including black out ones in a bunch of colors. I made the rails cover two full walls and got 4 packs of dark navy blackout curtains. They wrap both walls like a hotel room. Picture below is from their website to give a sense (although the ones in the picture are not blackout, but they do have some).
The whole project took 2 days, $350.
