H.E. Harris's prices were high compared to other retail stamp firms at the time, and the early 1980s in general were the high-water mark for most stamp prices.
There are some ultra-rare U.S. stamps that are worth much more today than they were in 1983, but most stamps are worth about the same or less. MNH Zeppelins are worth a few hundreds now, not $5K+. Almost anything mint post-1940 is worth face value or less.
You can get a Scott catalog a few years old for $20 or so on eBay
, if you want more recent catalog values.