@NautArch I don't really DM, but the Sane Magic Item Prices doc is a useful starting point, along with the
Discerning Merchant's Price Guide. The former only includes the magic items in the DMG; the latter includes all magic items released in (almost?) all books up to November 2018, though the creator said they don't currently have plans to update the doc (and that it's just a matter of priorities).