Mr Henderson,
You started to compare SolidWorks with Sketchup.
For true mechanical CAD the cheapest option is Alibre Pro
http://www.alibre.com/products/ad_compare.asp. It's not as mature as SolidWorks, Autodesk Inventor or SolidEdge, but it is also a lot cheaper than other mid range MCAD packages.
I will say again that Sketchup is not a mechanical engineering CAD software, although it can be used to make very neat models and schemes in PRO version.
For 2D CAD I sugest to check out fee
DraftSight from Dassault Systèmes the mother company of SolidWorks.