how much is a manga collection worth?

just a query. and I'm not talking about long running series like beserk or AoT, I'm more specifically talking about OOP titles. I have the full 27 volumes of excel saga, and individual volumes are hard enough to find, with some that are actually OOP or impossible to get. what could that fetch?
 
dang. this is the full english version too. it had a drop in popularity in japan during it's run so I can't see massive interest the anime was way more popular
 
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