Re: Which engine?
I think the difficulty here stems not from the classic 2 vs 4 stroke debate, definitely not country of origin, nor even the dubious quality control inherent with the in frame two stroke kits, but again & perhaps unsurprisingly - initial cost. The OP made their desires quite clear & unfortunately within those parameters there is to my knowledge only one kit that comes close to meeting all of them;
"I definately want a chain drive as I will be using a disc brake hub to bolt a king cog to, so the simplicity of the cheap 2 stroke motors is very appealing."
"I don't want to spend more than 200.00 on a motor, but am very open to a four stroke motor that installs the same way as the 2 strokes do."
"I definately DO NOT want a friction drive, as I believe from my experience in loaded touring, that is way too much weight on the back of the bicycle"
"So, which engine for around 200?"
As far as I'm aware, while you can get a cloned four stroke engine for around $200 - this would be an "engine only" sale, which while the OP stated that's what they wanted to spend on an engine, I'm going to assume they weren't considering a gear box, mounting plate, fuel tank, wide crank kit, sprocket, exhaust system, throttle kit & cables, chain & tensioner as separate purchases - which once included with the engine cost appears to be more than double the price they were willing to spend (if I am mistaken, please forgive the assumption).
Even setting aside personal mechanical experience & luck, yes - much can be said regarding the longevity and overall, long term cost savings of even the cloned four strokes over the least expensive two stroke kit money can buy. There is also much that can be done to reduce the cost of an in frame four stroke build, depending on your ability to fabricate, scrounge & repurpose components both new and used. Yet no mention of fabrication was made nor long term expectations and the fact remains that if the budget limitations dictate no more than $200 towards the cost of motorizing a bicycle and including the above stated parameters - there is only one choice I'm aware of, the in frame two stroke kit.
Everyone here has brought up valid points regarding the strengths and weaknesses of their favored engine type, yet I must advise caution regarding quoted costs. While you may indeed end up repairing or replacing components of the two stroke kit and it's important to mention that potential, the cost of all the components of a four stroke build must be included to accurately depict the initial expenditure, enabling them to make the most informed decision based on what they want and can afford. Neglecting to state the cumulative costs of all components needed does everyone a disservice.
If I am misinformed and you can get a complete four stroke kit that includes everything needed to motorize a bicycle for $200 - please do correct me, providing a source for such ofc. Were one to exist however, I would have to question it's overall quality & reliability as well as I believe what the bottom line is truly about is deceptively simple...
...what can you really expect from $200?