Good question. Following.

Any updates?

Most of the professionals that visit here use a CAD program so a lot more than $100!! DynaScape is a popular one. Otherwise Microsoft Paint works.

It depends on what you want the software to do. Personally, what I was looking for was something that could fairly easily do 2-D scaled layouts. That is out there. The fancy-pants landscaping simulating software is a different beast, and is going to be $$$$.

This is an old post but I am interested in something similar. Really just 2-D for my purposes. But also need to show elevation changes, like the old-fashioned paper maps did with stacked lines. I will checkout Dynascape as mentioned above.