Beginner with Experience... looking for "starter"

I’m an Electrical Engineer and have used some SBCs before (we have the X-Bow .Net boards at work and I learned the Motorola assembly language ages ago in school).

I’m a network engineer with some .net network programming background. I’m looking for something that can get me started that includes ethernet support… any suggestions, preferably <$100?

My end goal is to build an NTP Stratum 1 clock fed from GPS PPS…

Thank you.