That is pretty neat. I got my Beaglebone but haven't quite figured out what I am going to do with it. A GPS time server is a neat idea.
The price sounds about right. But, you also used your expertise, time and labor. Then add an enclosure box, documentation, support line, CE+FCC certifications and it can quickly get up there in price.
Oh absolutely, I completely get why folks sell them for $600 each. (They were $25,000 each at one time which I found to be rather extortionate). I used to run ntpd on my home server to keep the machines in my house synced until the reflection attack using it came out and folks were dragging down my cheezy home net using it to attack others. Now I only run ntp inside the firewall :-)
The price sounds about right. But, you also used your expertise, time and labor. Then add an enclosure box, documentation, support line, CE+FCC certifications and it can quickly get up there in price.