A rule of thumb for used (not wear items like clutches etc) goodies is 50% of new.
That % can go up or down depending on popularity, demand, & availability of particular item in the used market. Generally on an item that has a good intrrest level but is not seen used everyday the percentage can creep to 60 or 70%
Hope that helps.
If I ever sold mine, I'd probably ask for $110-130 maybe a bit less since I filed it a little to pop in easier. I noticed the price has jump about $10 for a new one since I purchased it.
Since it's just a tube that passes air, it's quality won't decrease very much over time. I'd expect people to want more money for it. You can also just build one just like it for a few bucks if you really want to save a lot of money.
It's still in the car, but I'm going to be putting in ab RX7 AFM so I have to get rid of the stock airbox. It's dirty but it looks like it's in good shape. Hard to get much of a pic while it's in there.