Mediator is the best way to go. you will need to get a tower case for it as well. The Mirage is built for it. Yes you can use cheap Ethernet card then. The best place to get it now is direct from Elbox. You will save a lot of money since they are offering free shipping. You could order the Mediator, The tower, the Ethernet card, even sound and video cards (I would get these off ebay). Yo will then neen MiamiDX or some other ICP/IP stack to get it all talking with the other computers as well as AmigaSAMBA. The site for Elbox is
www.elbox.com