Scrapbooks such as yours from that time frame can sell for $200 - $400 as a complete lot when offered at auction. If you were to sell individually, first check the feasibility of removing the ephemera and postcards from the scrapbook (i.e. are the glued down?) as change in integrity of the piece will diminish value. Though it may sound cliche, the best platform for you to sell these is on Ebay. It is where the most potential buyers would first go to search for such items. If you do consider selling individually, factor in the time and effort it will take. My personal opinion is to sell scrapbooks like this as a single lot after looking through and maybe picking out 1-5 standout pieces that can sell well individually and be easily removed.
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