If you're happy with that price thats all that really matters I guess. Value is what it's worth to someone and I know urgency sometimes dictates value. I am saying that used generators/stators generally go for less on ebay from what I've seen. I know this one isn't going to work on your particular model but this might give you an idea if you haven't been checking them out on ebay.
eBay Motors: Kawasaki KZ650 ZX750 KZ750 KZ700 Stator 21003-1083 (item 320282628585 end time Aug-06-08 18:54:04 PDT)
Since yours was used on the 87-90 model 750 ninjas it opens up the possibilities of finding one and if you find an ebayer thats parting out one of those models but doesn't have the stator listed you can always email them and ask if they have one.