Lemme give you a quick advice. Forget regging a "hacked" domain. The only time you should consider regging such domain is when you have quality service or product to offer on it. But even then, i would advise sticking to the big 3. Remember del.icio.us ? The switched to delicious.com long time ago. I wonder why..
The difference with del.icio.us and cocktaildress.es is the actual keyword though Tony.
The one that the opening poster is enquiring about is obviously of far superior quality in my eyes simply because it can be easily recognised as "Cocktail Dress" and I can see this going for a fair sum to a high end retailer in Spain.
I wouldn't be surprised if you can get low to mid $xxx
I notice there are a lot of people who are just plainly against domain hacks and see zero worth in them but as Sparhawke said, this reg doesn't need the extension for it to work.
Is there any sites out there that list domain hack sales?