I've been talking about doing this for a long time now, and I've decided to move forward with it.
For those who aren't familiar with what a CNC machine is, see this: http://www.youtube.com/watch?v=eLU_bdf2PEw
There are plenty of plans strewn across the internet on how to make one yourself, ranging from bathroom builds made out of MDF to workshop units made out of plexiglass (that look very sexy.) The plans themselves range from nearly incomprehensible to easy enough to follow, if you're mechanically inclined enough.
Conceptually, the workings of a CNC machine aren't complicated. You have three axis: left/right, towards/back, and up/down (z, y, and z.) Those dimensions of movement are each controlled by a stepper motor. The rest of the hardware is the table and gantry setup. The gantry holds your cutting tool, in my case a Dremel.
This thread will detail my foray into the world of industrialized production.
Portability. This means the unit could be easily thrown in the backseat of my car/SUV and taken somewhere. Not handheld.
Lightweight construction. The unit will be on the small side for a CNC machine, about 24" x 30" or so. Frame construction is 1/2" MDF.
I want this to be an open discussion. My progress so far has been to get the pieces cut for the table, assembly will happen either tomorrow night or Monday morning, depending on when I go buy the hardware.
On cost: your cost for this project will vary. Some of those who attempt these projects likely already have an assortment of shop tools, such as Dremel-like rotory tools, table saws, jigsaws, circular saws, etc. The major cost of this project will be the purchase of whatever tools you don't already have. The dremel is probably the most important, and possibly the most single expensive, tool required - it's the cutting head for your machine, and without it, you won't be doing any Dang thing once your machine's built. That said, once the machine is built, you will need some precision tools like a dial indicator to make adjustments for accurate machining. If you don't have ANY of these tools, expect to spend upwards of $500 for this project.
For myself, in combination with being part lucky and part already having ALL the tools required, my cost will be well under $200, if not just a tad under $100. I am at around $75 now, and at this point I could build the table and gantry assemblies, put them together, and only need to hook up the electronics required. I already have a power supply ready to go for the motors.
My best advice when building one of these is to read EVERYTHING you can find on homemade CNC machines on the net. At the end of this project, I will list the online resources that were the most help to me when building mine.
Edit: Will be updating this first post with required materials and tools as I go along, will post pictures of each as I go along.
1/4 threaded rods (3)
Long 1/4" nuts
1/2" MDF (2 panels)
1/2" metal wire conduit
1/2" metal wire conduit clamps
Angle brackets to attach MDF pieces
Various nuts and bolts
Table saw (or hacksaw, but... meh.)