hacking an AUI network port
I believe the AUI interface provides access to the Ethernet MAC directly. You might be able to make it talk to an older 10BASE-T switch, but it definitely won't work with a 100BASE-T or Gigabit Ethernet switch.

In modern devices, the MAC connects to what's called a PHY chip-- the chip that generates the MLT-3 waveforms required for higher data rates. Without a PHY chip (which is probably what those $30 adapters contain), it won't work.

But with an older switch, you might have a chance. The data might come out Manchester-encoded, which might be comprehensible to a 10BASE-T port. I'd start with the AUI description in Spurgeon's Ethernet book: http://books.google.com/books?id=VbTvnxBKzUgC&amp;pg=PA118