I Think in 2006 the Zx50 was Discontinued although some places still have parts available and some parts from other models are interchangable.
Some had electrical issues but im not aware of anything major.
I do know that some Gy6 engine parts will fit ie: magnto/stator/relays
One for 700 sounds like a good deal as long as its running up to par
The CDI units sometimes give problems but those are easy to upgrade to a better one.
but then again im nmot an expert at anything and usually break stuff
ps. if its near me i will buy it if you dont LOL