According to Justin Brooks' Primary Bibliography, it was published in September, 1984, by Chivers Press of Bath, Avon, England as a Lythway Book. It has 106 pages. Brooks' reference number is B86 (2).
There I can't help you. Normally, though, large print editions aren't worth as much as the "normal" editions, but in this particular case, I have no idea. I've never seen one for sale. (I don't have one, either, but I don't collect large print editions.)
This one seems to be very rare, there's one on eBay.co.uk for £47.99 (I believe) that's been there for ages. The seller seems very knowledgeable and says it's rare and is usually only found in the form of ex-library copies. Personally, I've never seen another one for sale (but then again, I haven't been collecting seriously for more than a year or two...).
I TEND TO DISAGREE WITH MR.RABBIT TRICK ON HOW RARE THIS BOOK IS AND FOR THE REASON HE STATED. THESE BOOKS WERE MAINLY MADE FOR LIBRARIES AND WE ALL KNOW WHAT THAT MEANS.LIKE HE STATES USUAL LIBRARY STAMPS AND MULTY READINGS FOR UP TO 25 YEARS AND IF LIKE OUR EX-LIBRARY BOOKS STAMPED DISCARDED. WOULD YOU WANT AN EX-LIBRARY EDITION IN YOUR COLLECTION? I`VE HAD MY SIGNED COPY FOR OVER 20 YEARS AND THINK IT`S ONE OF THE GEMS IN MY COLLECTION.SO IF guggenhe`s IS NOT AN EX-LIBRARY BOOK. GREAT BUY!