The Wrong Side of the Sky was his first book, published in 1961. The rights most likely reside with his estate (or whoever inherited) unless the book is highly popular and has been kept in print all these years (looking at Amazon this doesn't appear to be the case). Either a publisher would have to pay the estate for the rights or his estate would have to self publish the book to get it out there as an ebook.
The $200 'new' copy is just a couple of third party sellers hoping someone might bite at that price.
You could always buy one of the cheap used copies and scan/ocr it if you want an ebook copy.
More on the authors works...
http://www.fantasticfiction.co.uk/l/gavin-lyall/
http://en.wikipedia.org/wiki/Gavin_Lyall