I'm not trying to step on anyone's toes here but I'd like to offer another suggestion.
Have you conisdered buying some of the parts and making the others? The reason that I ask is mainly because of shipping weight. The JGRO router uses nearly one full sheet of 3/4" MDF and nearly one sheet of 1/2" MDF not to mention the nuts, bolts and gas pipe. I can't imaging shipping it for less than $80 with no insurance.
If you look in
Joe's Thread you'll see that is he offering most of the difficult to machine parts for sale. If you were to buy all of the parts he has listed, I think all you would have to do is cut out the wood parts. I managed to do that in one weekend using a low-end table saw and drill press. The really hard part (read time consuming) has been machineing the smaller parts (especailly the Anti-Backlash Nutes), and final assembly.
Another idea you might want to consider is the K2 line of rotuers advertised on this site. The reason I mention them is because of your budget. A realistic estimate for the materials in a JGRO router is $650 - $700. If you add your advertised $500 you're in the $1200 plus shipping range for a wooden router. On the other hand, the K2 machines start at $1150 plus electronics (and possibly shipping) for an alum. machine. (To be fair, to match the JGRO capacity which I believe is 38" x 19" x 5" you'll find yourself in the $3900 range). I looked long and hard at the K2 machines and in the end decided that the experience of building my own machine was worth the effort for me.
I hope this helps.