Another free alternative to Autocad is Draftsight. Draftsight is geared towards your basic computer drafting (equivalent to AutoCAD LT) and it will feel similar to older versions of AutoCAD. AutoCAD comes in many different flavors but now emphasizes its modeling capabilities (despite its 2D drafting roots). Sketchup, in my mind, has always tried to be the 'easy' 3D modeler, and although its capabilities as a drafting program are sometimes disguised by the interface, it can be powerful in its simplicity.

Also, I am not sure where you are at, but if you are in the US (and the survey is too costly) you might be able to get some elevation data on your land from your County. Maybe try their website for GIS maps, and see if they have elevation data. It won't be be exact (2-ft or 5-ft contour lines at best), but it could give you somewhere to start when compiling your own data.

I am also interested in how this will turn out. Good Luck!