Great-Grandad and the vanishing glacier is now for sale in selected bookstores in Iceland, Germany and Spain. The first and obvious choice is to buy a copy straight from the author in a guided tour. This is not necessarily the cheapest option as the author charges travelers either $30 or €30 for signed books. This is roughly equalant to what an unsigned copy costs in local book stores in Iceland, 4-5000 Icelandic kronas. An alternative souvenir shop, The Heart of Reykjavik on Laugavegur 12b offers the lowest retail price, 3900 Isk. A major retail store that Forlagid Publishers runs on Grandi has it for 4190 Isk. Forlagid is also your best bet if ordering an english copy online.
Eymundsson, The larges book chain in Iceland is selling copies for 4.999 Isk in their stores in Reykjavík, Akureyri, Selfoss, Ísafjörður, Húsavík and Westman Islands.
You can also find the book in popular souvenir shops in Gullfoss, Thingvellir and Vík. As well as in Sveitabúðin Una in Hvollsvöllur, an excellent retailer of local Icelandic handicraft.
German and Spanish speakers can find Great-Grandad and the vanishing glacier for a slightly lower price in their native countries, the price being adjusted to each market. Libreria Proteo in Malaga is selling Spanish copies for €16. In Germany the book is available for 20-24 Euros. You can find it in Pankebuch in Berlin Pankow and in Stotieks bookstore on Richard-Wagner-Straße 39. Last but not least you can buy it in German online stores. Isi4fun has it in stock for €24.