Go to the mobile install bay at your local Best Buy..... they sell the whole thing (mast, motor, the whole unit) for about 50 bucks I think. You can install it yourself - it's very easy (since it's located in the trunk), all you need to do is make sure you connect 3 wires the right way. 12 volt constant, 12 volt switched, and ground.

The ones Best Buy sells can blast through ice, mud, and anything else.... they use strong mechanics and higher current motors than most factory antennas.