Hi,
I have a 730, and am fixing to buy a 1090 from a friend. I've heard many, many wonderful things from folks who own 830's - the original 830, that is, not the $12,999 variety. They are in such high demand, that's one reason they are going for so much on ebay. If you find one for under $500, it's probably a deal. I've seen them run upwards of a $1000 at times. I believe there were two varieties of the 830, a totally mechanical one and one with a circuit board, or was that the 930's. Oh dear.
Tell ya what, tho. There's an awesome Yahoo Group called the Bernina Thirty Somethings, originally started for owners of a X30, whether it was a 530, 730, 830, 930 - you get my drift. I belong, and have found them to be wonderful folks, very knowledgeable and very helpful. They'll answer any questions before or after you buy a Bernina and also help you with any maintenance or usage question you might have. As well, they have a nice database of helpful information, too. Best of luck to you. Once you've sewn on a Bernina, you'll love it and understand why so many folks want them and won't sell them once they do have them.
Happy quilting,
Karla