These are potentially a great item to find. Stereo cards were very popular in the late 1800's and early 1900's. These cards were produced by Underwood and Underwood and came in various boxed sets. Collectors will pay a premium price for boxed sets that are complete and in good condition. Full sets will sell for $200 and up. This particular set that depicts scenes from Egypt is worth over $500.
Don't make the mistake of bypassing single cards. Although most cards are worth a few dollars each some individual cards can reach into the hundreds and even thousands of dollar range. The typical viewer is worth around $40. Stereo cards and the viewers can be found just about anywhere. So keep your eyes open for these sure fire CASH IT items.