AutoCAD vs. ProEng.
<< Pro/E is a 3 dimensional parametric solid modeling CAD program. As such programs go, it is very capable, >>
You see, ProEng and Autocad do not play in the same league.
In the small league, AutoCad is much more a drawing software and it does 2D or 2-1/2D but never really reaches the 3D as such.
Whereas ProEng plays in the pro league since it competitor are CATIA, IDEAS, SolidWorks. They have been true 3D modeling with real volume and even solid rendering. From them, you have simulation pckages which aloow you deep anlysis. You can even link to finite elements.
AutoCAd should a lot cheaper but its purpose is simple drawing exchange in maintenance departments or the like.
ProEng is more the long term design of very complex systems liniking to detailed part design and analysis as well such as found in design and engineering offices. Then, the price should be quite higher.