Short Version of Question
I am pretty confident that I can write the g-code to make the parts I want to make. However, I would like to have some sort of check on my newbie tool-path before I waste my friend's time on his CNC machine. I have not had much luck finding a software tool to use to visualize the tool-path.

What is the most affordable option for hobbyists wanting to visualize a g-code toolpath?

OpenSCAM looks like it was supposed to be exactly what I want. Unfortunately it crashes every time I edit the tools or save a project.


Back Story In Case it Helps
I am very very new to CNC and I know that I probably don't even know the correct questions to ask. So here is the context of my question in case it helps.

I am hoping to build or buy a CNC router next year. I can just barely afford a machine but cannot afford to spend lots of money on software too. I definitely cannot afford the CAM software my friends use on their CNC router (costs $1K+). So I am trying to do a proof-of-concept that I can do an end to end workflow from idea to design to gcode to cutting.

I've looked at some of the affordable CAM software packages. The parts I am cutting have a number of tool changes for different types of surfaces but the patterns are all nice strait lines or circles. Quite frankly I am fairly confident it will be easier to just hand write the gcode than to duplicate the design in the CAM software after designing it in CAD; even after allowing for finishing passes, etc. the commercial CAM packages seem to add very little value for my application... except they allow you to visualize the generated tool path.