You said you're looking for something that is inexpensive.
The question is whether you want to be able to see the blackdrop in your image or do you just want to see complete black/darkness behind your subject.
If it is the former, then it is hard to get away with cheaper materials without them looking cheap. If it is the latter, then you can get pretty much anything, manipulate distance to background, light your subject a couple of stops or so over the bg, flag off the bg and so on to get the result you want.