I've only seen 2 for sale the whole time I've been collecting. (Then again, I only looked for it for a short time, but when searching through Ebay, I wouldn't stumble across it.) I think the 2nd edition Dream Castle (lavender version) used to run around $30-$70 and has even been known to go for $100 on Ebay before. Prices might be different now.
You have good tastes, it has such pretty colors! I wanted it, but I am just as happy with my 1st edition, mostly because it was like that in the cartoons.
ETA: good to see you back, I remember you because of your name, I think you said you named that mystery pony in Firefly's Adventure/Battle at Midnight Castle Far Dreamer.