Green screen, lasers, lightsabers etc

I need a space background for my spaceship set and i think i will use green screen, but is there a free program for green screen that i can use (or like $30.00 or lower)? Please help me with this. Also, how do i make laser effects and light sabers and stuff like that? I don't have any problems with sound, just need to know how to make cool looking lasers. If you can give me an answer to any of these two things, please let me know!