There are SE/30 ethernet cards and there are SE/30 accelerators and there are even SE/30 graphics upgrades (the Micron XCeed being the pick of that particular litter), but they are rarities and, as the machine is prized by collectors, they are accordingly expensive. Some are very expensive. There are even ways and means to have at least two of these at the same time installed in an SE/30 without too much hacking, but the requisite adapter board costs yet more money.

A recent eBay auction for an MacCon ethernet card for the SE/30 went for about $70, though prices vary and I have also seen one fixed priced at $140 or so (and not sell, so far as I know), and another one go for $40, all just in about the last four weeks. It "pays" to watch the auctions.

I will likely be selling an SE/30 ethernet card on eBay in the next few weeks, with the hope of hitting somewhere around that magic $70 mark. If you want to make an offer.... I have three MacCon cards, so selling one or two at a good price will allow me to collect some other goodies (e.g., an accelerator) that I do not have, without actually spending any money. I also have recently acquired three different SE/30 video cards for driving large external monitors of the period, but have not decided quite what to do with them. Some details here.