Building an Integrated hovercraft, Need fan help!?

Okay so here in my section of North Carolina we have to do a senior research project in order to graduate and i have chosen building a full fledged racing hovercraft ( I aspire to being an aeronautical engineer ). My hull material is made of rigid foam insulation board covered in fibergl. And since I'm on a tight budget I'm using heavy duty poncho and vinyl shower curtain for my skirt. I am using a 1972 Suzuki t-500 dual carb two stroke motorcycle engine that has 47hp @ 7,000rpm. My biggest question is on the fan. Obviously a hason wing fan would be ideal but $200 dollars is a little bit out of my price range so I'm looking for alternatives. It needs to be some sort of composite material so that if it flies apart at 7,000 rpm's it wont slaughter me (hopefully) and it needs to be cheap and easy to find. What I've been considering lately is a radiator fan from a tractor trailer. It needs to be 36 inches (at least), so I'm wondering how large an 18-wheeler's radiator fan is?