DH used to do a lot of green screen video effects. And lots of inserting lightsabers into kids hands.
There is a reason green screens are day glow green... it's much easier to separate the subject form the background. If you use a white background hair and fair skin can be hard to pull out. If you're just wanting to play, start with a few yards of bright green felt or bright green craft paper to shoot against. It's very cheap (I spent like $10) and then you can take the shot, easily remove the background and put in what you want. Don't buy a fill, play around and make your own or find an image with a creative commons license that can be used for that.. check devinatart.com and you'll likely find something.
you don't have to invest much to find out if you will like it and if you do like it you can always spend more to do it better.