I'm sure there is (or was?) a low-cost MIPS board with four gigabit Ethernet ports. I can't find anything about it now though.

EDIT: this was it, the Ubiquity Networks RouterStation Pro http://www.ubnt.com/rspro ; it was the basis of an official "MIPS Linux Starter Kit" http://store.mips-store.com/mips-linux-starter-kit.html which is now "[t]emporarily out of stock". 1 × USB2, 128MB RAM, JTAG, no video. $79 USD MSRP.