Value is hard to say.....but a couple of points...
Benelli Ultralight model is not very popular among sporting clays, skeet or Trap shooters.../ they come in 24" or 26" barrels / and in 28ga , 20ga and 12ga....and they weigh from 5 - 6 lbs....
Many of us - as experienced shotgun shooters - find a gun that short and light to not be very functional / with light and short guns - most of us tend to "slap" at targets or live birds ...vs making a "smooth" shot with a good follow-thru...
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Benelli in general has some light guns....even their Super Sport model, which is a good all around clays gun ...with a 30" barrel in a 12ga is only around 7 lbs...and the legth ( at 30") helps smooth out that gun swing as well...where many of us like shotguns up around 8 lbs - for good swing characteristics.
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I think the Ultra Light models in my area are selling new for around $ 1400 ....and I can't imagine used, it would be worth more than $ 800...and personally a gun that light and short - has little, if any value to me personally... I wouldn't want it at all...not even as an entry level gun for a young grandkid or something....
But it does have value ...if someone wants it .../ you should really check with gunshops in your area...gun values vary a lot with different areas of the country ...