Indeed Sketchup is still free, though is now named "Sketchup Make". The software was acquired from Google by Trimble a few years back. This seems to have been a good move, as the original development team was retained and it is being actively developed.
"Sketchup Pro" is the commercial version, and has additional layout features for CAD print and other types of presentation. It retails for about $600, which is quite competitive when you compare it to AutoCAD (but it is nowhere near as capable), i.e they did not kill it like Microsoft killed Caligari trueSpace. There is a student version of Pro for qualified students and instructors - a one year license which costs $49.
One thing about the Pro version that bugs me is how little in the way of quality models and extensions are included. The better library models are from 3rd party developers and cost in addition. This adds a lot to the cost if using for CAD design or presentation. I wish, for instance, Trimble would package a useful and accurate architectural library of models (doors, windows etc), much like the Home Designer software does. That said, there are a lot of free models on the Sketchup 3D Warehouse ( https://3dwarehouse.sketchup.com
) but Trimble has crippled the model review system so it is really difficult to assess the quality of a model - a door or window model for example. Are the measurements right, or just based on somebodies uneducated guess of measurements? Unfortunately more often than not, the latter is true, and there are some really bad models out there that look great.
One other thing - if you open and save your Sketchup model in the latest version (v. 2015), it will not be backwardly compatible after that. You are committed to the current version only. If Trimble ever decides to start charging for Sketchup Make (who knows?) you will be stuck.