If it's just about modelling I'd go for
Wings3D (freeware) or
Silo. They're both pretty slim packages and should run on pretty much everything not really ancient (although imo the attitude that you only can use old software is kinda wrong - modern software lets you do some insane things but much of it got possible by better optimizations, the editors themselves don't need THAT much ressources - just those huge projects will do)...
If you want to do more than just modelling itself have a look at
Blender (freeware). I'd use that instead of buying something "outdated" like a really old version of Cinema4D. Here you have some advanced tools that were developed to make your life easier and more efficent - you also have pretty much every modern feature or file format this way too...
Enjoy your meal
Toast