The cheapest Sony network adapters I can find are $10 without shipping on ebay.comIts more of that I already have a 32gb CF card which is probably plenty for the 10 or so games that I own.
Its a bit odd - an original Sony IDE and network adapter by itself is about $20. Adapter with rails and an old, slow, soon-to-be-dead hdd is $50. But I can't find a cheap price for either adapter + rails - hdd or rails by themselves.