"Readers copies" of the first edition are frequently available through book sites such as AbeBooks or Bookfinder.

A "Reader's Copy" is generally a former library copy or personal copy without a dust jacket. These are sometimes available for as little as $10.

A copy like the one being offered is worth more, because of the dustjacket, but how much more is difficult to say. From the photo the dustjacket appears to be in the "fair" category with a sticker still obvious in place and the mark from one being removed in the upper right corner. These things detract from what would be offered by a collector. No mention is made as to whether this is a former library edition, or whether there are any interal marks, which would also detract from the value.

"Handbook of Model Rocketry" editions 1 thru 5 were printed as both hardbacks and paperbacks but editions 6 & 7 are paperback only.

Rarest of the Handbooks are the paperbacks of the first edition (which I have only seen offered for sale once), and signed versions of any edition which rarely come up for sale.

G. Harry also produced another "Handbook" in 1970 called "The Model Rocketry Manual" which was published in paperback by Sentinel and then reissued in 1977 as "The New Model Rocketry Manual" by Arco. If I remember correctly this was authored as a result of Stine's association with a rocketry company (MPC ?).

Many rocketry folks are unaware that G. Harry Stine was a prolific author of both non-fiction and science-fiction (under the pen name Lee Correy). Virtually all of his work (including Star Trek #6, The Abode of Life) is still available at very reasonable prices through used book dealers.