I saw a used Tenor Black Nickel Keilwerth SX-90 on eBay for around $550! I don't know how good it was of a horn, but I do know they sell them on eBay. Where do you live? Are there any music stores around you that sells the instruments?
I know of a place called Dominics Music I think not to far from Boston that sells all sorts of horns..if you wanted to look into that.
Hope this helps