The way I got my bowflex was ebay for a couple hundred, new in the box even. The story I got was it was a gift from a girls boyfriend and it made her so made she just wanted it out of the house...lol. But something like workout equipment I do not have a problem with buying used as long as they work. I even seen them at second hand shops and on craigslist all the time. People get them and then they just sit so they want them gone.
As far as once you get them, I ran through the rods that they come with fairly easily so I had to get the add on box to add a couple more 50# rods. But these machines to me are not meant to be used to bulk up with heavy weights, they are great for getting in shape and staying in shape.