This could be something that you bought for a higher price than what most people would guess based on the item, or it could be something you bought for a normal price that has gained significant value as time has gone on.
What made me think of this question is a LEGO minifigure I got with my "The Hobbit: An Unexpected Journey" disc. It is Bilbo Baggins in a blue coat that was apparently only sold in that movie box only at Target stores. Even considering the exclusivity, I would have guessed maybe $10-20 for such a tiny piece of plastic, but there are sold listings on eBay from $80 to $225. I could possibly even get towards the higher end of that number since I still have everything in the original box in good condition. It's not worth a ton compared to some other items people may own, but I think most people would not expect nearly that amount.
What do you use the servers for, if you don't mind me asking? I've been considering setting something basic up for some additional file storage or local media streaming and am always curious what others use their setups for.
I used to work IT for a while and we had one guy who would pick up all our old hardware from clients. A lot of it was still functioning well, but the clients got new tech and wanted us to just wipe the drives and get rid of it. The guy would sort through it, keep some of the stuff that was functioning either for himself or to sell and would strip the rest for materials.