SketchUp is a simple, user friendly yet powerful 3D modeling software which is very reasonably priced at around US $500 (considering other 3D modeling softwares are priced at +2000 US$). You can try out an 8 hours free trial version; 8 hours does not mean it expires within 1 day, it means 8 hours cummulative usage of the program. Before you start, download and view all the Macromedia Flash tutorials and very soon you will get the hang of it.

http://www.sketch3d.com/