I've got a budget of around $200 I'm 6' 4" so I'd like a larger bike. I'd also like a bike that won't take a lot of modding to put a chain drive motor on it. I'm about to hit up our local used bike shop, but if there's something new in that price range I'd rather ride shiny.
All I can say is don't get a $100 Huffy Cran
broke, the rear wheel bearings and coaster brake suck, and it's hard to mount a sprocket to them.
A quality coaster brake bike is fine, I like Macargi's like the Touch.
It's a bit small for you but I'm 6'2 and it's not uncomfortable to ride.
~$180 with a front C-brake.
The rear sprocket goes on easy and you can you mount the engine nice and low, down to the pedal chain guard, the seat post is the perfect angle for a level carb and they have a pretty comfy seat.
One of my staple 'cookie cutter' builds because they don't come back for repairs.
The kits flat U-bolt mount will work but I recommend you buy a muffler clamp to replace the U both for a 380 degree grab and flat spot, I use $8 SBP front mounts for a bit more flexibility (they come with a bunch of spacers and hardware) and strength but not a necessity.