Castles are popular, but don't forget that we already have some for sale. Pirate ships would be second in interest. Houses are nice, but I think you might be too limited because houses are so time period specific. Modern aircraft, especially high poly, would appeal to a very limited audience. There are people out there who could really use them, but most people here prefer Sci Fi and Fantasy to modern. You might do better with Sci Fi ships instead. The prices listed above aren't too steep for me, but I'm spoiled and have no life outside computers. Most people do silly things like eat, go to movies, etc. and the price would cut into their budgets. It seems like a lot of people budget for 1 - 2 items per month, so up to $40 in Poser spending per month. Your stuff would be 2 months, minimum. (I'm not saying it wouldn't be worth it, but it would make people think long and hard before buying.)