No one can tell you, each time you have to do a little research like checking for similar prices on e-bay, bentrider, rtrmag.com, recumbents.com, and of course craigslist. Probably this always takes 30-60 minutes but will give a good look at advertised prices.
For craigslist, there is a good tool for searching all of craigslist, or craigslist within a distance : searchtempest.com when you search on a keyword in there, after you set a search distance, like 500 miles,then click on open all. It seems like a lot, but if you hover your cursor on the close window x, you can quickly look at each local craigslist (maybe 20 or 30 of them) and see if anything close to what you are selling is for sale in a local craigslist.
Of course, in all searches using the word recumbent, it's kind of annoying but you have to work to eliminate the stationary bikes.
If you are not willing to do that kind of work, then used bikes in great shape are generally in the range of one-third to one-half their initial value depending on age and popularity, but really about one-third seems to be the norm to me for recumbent bikes. It's why I always advise people to buy used instead of new, especially for their first recumbent while they figure out what they like or dislike as the resale of the first recumbent does not then eat their capital.
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