I've put my Nokia N950 Pre-Beta 1 on eBay: http://www.ebay.de/itm/132042020412 If someone from the forum is interested, send me a PM please.
How could you tell it is a Pre-Beta if it is of black color, not silver? Please post the number written on small "S4.0 HW1124 XXXX" sticker under the battery, or make a photo of it: