The Turnigy SK engine is also a good deal. I have seen it fly and it has just a little more power and stays cooler generally. Also it's possible to fit that in exactly the same manner as the Hacker, including the back bearing.

Only downside to that engine is that after purchase you have to check it; are all the magnes glued correctly, and so on. But if you give it some care before first usage, it's a better engine for the WindS 110 than the Hacker.. and that for like 35~40 dollar.