I added some dimensions to my main drawing. See page 2
http://www.buildlog.net/cnc_laser/drawings/main.pdf1. Cutting area is about 14.75 X 24.5. The table can fit bigger material, but that is about the largest range of motion.
2. The overall size is about 28 x 49. The plywood sides can be cut from 48" wide material.
3. I probably spent about $300-$350.
4. My fan is huge and loud. It does a good job. You might consider pulling air through the work table. It will hold down light materials.
My machine was just designed as a learning exercise. I would probably do a few things differently, if I made a new machine. I would probably drive the gantry from both ends.
It has held up well though and I have only adjusted the mirrors once, but my current method is only suited to small lightweight gantries. The only issue I had once is a tiny piece of some material was on the right Y rail and caused the bearing wheel to ride over it. This caused a little .03" bump in my cut as I went over the thing. As the end went up the beam angle changed and caused the deviation. Once I clean the rail, the problem went away and I watch out for that now.