That's a tough one. The DT240 adds quite a bit of value. It's the rim profile and whether or not it will support tubeless that is the rub. If you don't have any other prospects and don't intend to run tubeless, I'd venture to say $100 is more than fair. If you intend to run tubeless and the rim won't, then I'd say pass unless you already have a nice modern aero profiled rim to lace the DT hub into.
TBH, to me the value is the hub.
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I shouldn't have to "make myself more visible;" Drivers should just stop running people over.
Car dependency is a tax.