ME's scoff at the very existence of Sketchup, but for a free modeling tool, its good enough.
If you like something more programming oriented, OpenSCAD is great for parameterization. You literally code your 3D model.
Neither of these tools comes close to something like SolidWorks, but they both get the job done.
A 3D printer is probably the easiest and cheapest method of fabricating your designs, but the ability to make functional parts is fairly limited
Sherline sells a small tabletop mill for something close to $1000.
Grizzly sells a bigger one for $1300.
Both of these can be retrofitted for CNC for around $2000.
There are now 3 offerings of complete tabletop CNC mills for $2000 to $2500 (Nomad, Othermill, and Carvey)
If you can program, learning GCode will be a breeze.
CAM is probably where most of the learning curve lies. This is where machining knowledge is most beneficial.
If you are lucky enough to live in certain metro areas, Techshop has several locations across the US. Its essentially a fitness club but with machine shop tools instead of exercise equipment. You pay a monthly fee, and you can use everything. They have several different types of CNC machines, as well as training.