How comfortable are you with Facebook Marketplace? I bought my N2DSXL off of their a few years ago for around $100. Mind you, this is circa 2021, in-person, and in a fairly low cost of living area, but good stuff like that can be found with sufficient patience. Lots of kids that grew up with these systems are offloading them as they approach/enter adulthood and will likely continue to do so over the coming years. On top of that, being able to inspect your product before actually paying for it is huge.
On the other hand, if you need shipping, maybe stay away from FBM unless you can find either a) an extremely reputable seller or b) a listing with the "Checkout on Facebook" option. The latter offers low-hassle purchase protection comparable to eBay's, whereas paying off-platform gives you very little in the way of assurances.