You can probably get a good idea of price by registering at patternreview.com and doing a search on Brother Innovis machine reviews. Most reviewers provide the actual price they paid for their machine. Pay attention to dates on those reviews so you get an idea of current rates.
Edit: I actually went there and looked, but couldn't find any reviews for those 3 model numbers.
Edit 2: found this "sold" listing for a slightly used 900 on eBay:
https://www.ebay.com/itm/Brother-Inn...UAAOSwSwVaamoD