I've trawled through a load of eBay sites around the world to see how well The Battle of Alamut sells.
First off I separated the new, unopened sets and the 'built but complete' sets and disregarded any with bits missing or without boxes. The results, below show a wide variation between continents. There were no 'as new' sets sold in the UK recently whereas Australia ONLY has new ones, so the results aren't as complete as I would have liked. The values are an average of all sets sold.
UK - used - GBP = 32.93 (which equals $53.47 or E40.76)
US - used - $ =40.81 (which equals GBP25.13 or E31.11)
- new - $ = 56.97 (which equals E43.43 or AU$54.11)
Europe - used - Euros = 49.17 (which equals GBP39.72 or $64.50)
- new - Euros = 85.07 (which equals $111.58 or AU$106.00)
Australia - new - AU$ = 96.10 (which equals $101.15 or E77.11)
If you can work out my mess of calculations it shows that the USA is by far the cheapest (as probably most people suspected anyway!), with mainland Europe the most expensive. Sadly I couldn't make a direct comparison between Australia and the UK.
I shall try a Star wars set next time as they are far more popular than Prince of Persia and I should get many more results.