See strida site for cost of upgrades. I bought a used strida. They will start selling them again in the US, It might be better to wait.
As to the Strida 3: I have to replace the folding handlebars, they are held in place by soft metal pegs that wore out (Item still in transit from UK); wrapping electircal tape around the handle bar is a temprary fix. Some minor hardware was also missing and replaced. The metal wheels are not that good, I had to true them, maybe plastic is better for 16" wheels.
2000 Montague CX, I do not recommend it, but still ride it.
Strida 3, I recommend it for rides < 10mi wo steep hills.
2006 Rowbike 720 Sport, I recommend it as an exercise bike.
1996 Birdy, Recommend.
Wieleder CARiBIKE (folding), decent frame.