Okay, why do you want to spend time compositing in post? How are you going to deal with the green cast that the screen will cause, especially for people wearing white/light clothing? On roll of seamless grey gives you white, black and grey backgrounds, with a quick adjustment of exposure. You seem to be doing this as a commercial venture, so I'll reiterate: Don't go cheap. If you don't have the money to buy at least decent quality, DON'T BUY ANYTHING. Junk, and I do mean JUNK such as Cowboy Studio produces will cause you grief sooner rather than later.
Without meaning to be rude, do you even understand enough about monolights to know what features to look for? Do you know which ones have easily available & replaceable flash tubes? Adjustable modeling lights? Whether or not they're auto-dumping?
If you absolutely must by cheap, than look to something like the Flashpoint series by
Adorama. They're cheap, but they're at least decent. You also need to face up to the fact that photography is a lot more than a camera. Photography equipment is often large, bulky and heavy. When I go to do a location shoot, I bring a dolly. I can make six-eight trips from where my truck is parked to the location with gear. Typically: two or three camera bags, two lighting cases, extra stands, clamps, etc, background... if you're trying to squeeze this all in to one small shoulder-bag, you're not going to. Again, not trying to be rude or cut you down, but there are some realities to face, and it strikes me as if perhaps you need a little more experience.