Aperture needs the originals, if you want to export the edited versions, because the versions will always be created from the originals. All you can save from an Aperture library, if the originals are not available, are the previews.
To see, which files have been affected by your "space saving" strategy, ccreate a smart album with the rule "File status" is "Missing".
Thsi should show you all images, where you have deleted the origiginal file.
To save the previews from this album, select all thumbnails in the browser and drag them to a folder on the Desktop (or better on your external HD). Now you can try to reconnect the images in the "missing" album to the saved previews.
See this manual on how to reconnect: Aperture 3 User Manual: Working with Referenced Images; scroll down to the paragraph "Reconnecting Missing or Offline Referenced Images"
Added: Alternately, open your Aperture library again in iPhoto and try to export the versions.