As mentioned in the other thread, an essential reference book is the SCOTT Specialized Catalogue of United States Stamps and Covers
. If the collection excluded this book and if stores are sold out, perhaps borrow one from a local public library. Also as previously referenced, StampSmarter.com's 1847USA
online identifier is helpful.
In the United States, the norm for referencing these stamps is typically the SCOTT number. Thus, knowing the SCOTT number is typically a prerequisite to determining the value. As this is a postage due stamp, we know that the SCOTT number will have a "J" prefix.
On the StampSmarter.com website, I clicked the "Back of the Book" (BOB) link. Basically, anything beyond a standard postage stamp is in the "back of the book." From there, I clicked on the Postage Due 1894
link. That page lists all the varieties of this stamp and respective SCOTT numbers.
When you see a value in a catalogue, take it with a grain of salt. The actual monetary value is dependent upon finding a willing buyer. Assume that if you sell this stamp, it will sell at a fraction of the listed catalogue value.
I hope you find stamp collecting enjoyable and choose to keep it as your hobby. Relax and enjoy.