You'd have to have REALLY good luck to find an external HD/RAM expansion for those prices online, so keep an eye out in local trading posts and newspapers.
For a brand new solution, you could contact the maker of these boards and see if he's willing to make and sell you one. It would be really handy if he'd make a whole run of them, I'd certainly get a few for my A500s if I could afford them.
http://www.students.tut.fi/~leinone3/ide/ide68k.htmlGood luck!
