Switching to Unity does seem to be a new trend which means any GS version is going to be difficult to get a fair price for or even sell at all. As others have pointed out; I'm keeping my GS and using Unity as well for level designing just like I use MED, Blender and Milkshape for modeling. GS is still an amazing tool for the price and the free upgrades make GS an even better value; Unity Pro sells for $1,500.00 and the developers charge $500.00 for additional upgrades. The free version of Unity is missing many useful additions like real-time shadows.