What is the value of an old autoclave?

Its value will vary, and will be set by the market (the need). The best idea is to check online auctions (eBay) for similar units, and then check companies that sell used scientific, medical or industrial equipment. All this involves web searching, and for someone not at ease with this kind of thing, here's a chance to practice. It's a really good idea to be able to search the web and refine the Wording in search arguments to get optimum results. It's like driving a car - there is a high pay value in learning to do it.