You can pick up a camcorder for cheap. The Flip is 100 quid for their nicest camcorder. It records in HD and stores 2 hours. It is by no means professional but you can pick one up for 50 quid if you wanted to and see if that meets your needs. DSLR is the way to go but you don't want to buy something you don't need and spend a ton of money on it(or maybe you do, I don't know you). I can't vouch for a camcorder's green screen ability but it could probably take care of most of your needs for lots cheaper.