How do you estimate an items worth when you don't have anything to compare it to?

I don't know what it cost new back then; I don't really know what it would have been worth when i got it (kinda a gift/trade type deal). I can't find any "red apples to red apples" comparisons (ebay, etc...); so I don't know what I could sell it for.

Any ideas?

It's a old Q-Logic box...

...with two oldschool 10-inch RF Punch's (not sure of the version or impedence).

I used that setup in a certain vehicle because I don't drive it that much (in winter, I hardly drive it); and, I needed room to but more stuff in it (tool bag, cleaning accessories kit, "junk drawer" bag, spar parts, and other things. Gonna sell the vehicle soon so I need to empty it out. If I include it with vehicle (selling to a private party), I still would like to know it's value.

Whatever someone is willing to pay. Those items scream Craigslist to me...