Jenkly

Dr. Who?
 
You mean the character portrayed by Matt Smith?

The "cheapest: camera for "perfect" green screen work?
Simple, The Blackmagic Cinema Pocket.
Obviously you can do chromakey work with 4:2:0 cameras, this has been done for many years. but if you really are looking for the cleanest key do you need at least 4:2:2 and more if you need to key hair and translucency.
My basic needs for a good key are:
1. Lighting and subject isolation without spills.
2. Sharpness

4:2:2 is all you need. It sounds like people are trying to give you the best here but not taking into account time management and affordability as a whole package. Most broadcast is keyed with 4:2:2 cameras. You still get definition around hair and fuzz. It is completely manageable. I would never go back to 4:2:0 after working with a live digital key, you notice the difference instantly. Yes the G6 is a great camera, yes it is adequate, but you are going to get more value out of the bmpcc.

Obvious choice in new lenses is the Rokinon 85mm IMO, in either photo or cine versions. Both versions are running under 300. You might be able to get something decent used for less though.

This raw hack has whipped me up into a frenzy. I started shooting stills years before video and became very used to working with raw files. For my entire time filmmaking I have been irritated that I'm forced to shoot in a compressed codec and suddenly I am presented with a camera that shoots raw that I could swap to for no money? Seems like a no brainer.
 
The ML team have unlocked compressed video on the 50d too and it has a nice enough image from what I have seen.
 
I shoot narrative mainly, so a super 35 raw camera for £350 is a dream come true. Even several of my lenses will become more easily useable. At the moment I have to quickly put the lens on a Canon body to set the aperture, then put it back on the GH2. I only swapped to the GH2 a few months ago because I wasn't happy with the mush the 550D was giving me. Prior to that I have had a 10D and a 30D so you could say I'm a bit of a closet Canon man really. I just hate the way they tier their products based on arbitrary firmware implementations and minor hardware difference.
 
It's now even more obvious than it already was that the camera manufacturers all have a meeting once every few months to decide which feature they shall all implement next. The progression of the technology is far to linear across the manufacturers. BMD have clearly broken the mould and I praise them greatly for doing so. 

I did a lens cap test.  (actually made a video too)  The noise/grain has a very consistent ascent.  I'm not sure how accurate these tests are but I remember watching one where they used the GH2.  This seems a bit more consistent.

I hope I understood you correctly when you asked about trial videos at a lower ISO.  I know I already posted this response on Vimeo but I just wanted to reiterate it in case anyone else was wondering.  The Extended ISO does not seem to translate to video, only pictures.  But the ISO Increments option will get you more ISO between 200 and 6400.
 
Thanks for the response!  I've been watching your videos.  Wonderful!

Here is a little tutorial for getting some extra ISO options on the GH3.  It gives you two more ISO values between the ones that came preset with firmware 1.0.  You just have to enable them.  I'm not sure how widely known this trick is. I keep seeing ISO tests showing off ISO 200, ISO 400...etc. and nothing between.  So, I hope this helps!
 
https://vimeo.com/62399018