Just to reiterate - mesa has quite a few solutions that replace the printer port for < $100. These are not buffered solutions but realtime. (And almost unlimited expandability)
Ethernet support in linuxcnc is pretty new. (I have been testing for atleast a year now). The next release version of linuxcnc gives you ethernet support + the new trajectory planner-thanks again Tormach! (among other improvements). V2.7 is darn close to release - testers welcome