The UniDisk 3.5" isn't the only option for a ][+/Europlus or //e. Under some configurations (RAM and ProDOS version), all can use the SuperDrive controller which supports any 800KB drive plus the 1.4MB SuperDrive. Officially the SuperDrive controller requires a //e, but allegedly it will work with older upgraded Apple ][s. However, both UniDisk 3.5" and SuperDrive controllers are rare, so buy whatever you can find at a sensible price.

Almost all vintage ][ software was written on the assumption that the owner had one or two 140KB floppy drives. Software that is now written for the ][ family assumes that the owner is an enthusiast and has a high spec ][ with more storage. This isn't a total calamity. There are affordable hard disk/flash disk alternatives to the collectable vintage controllers and disks.