The video standard for pre-HD DVD movies (MPEG-2) is not space efficient and as mentioned, dual layer blanks cost ~20x single layer. If you want to fit more on a disc move to MPEG-4 compression: XviD, DivX, et al.
Look into Auto Gordian Knot as a quick and easy converter. You won't retain the original disc layout or menus, and it does take time, but it's much more space efficient. (~3 movies on a single layer DVD with very good quality).
Here's a guide:
http://www.doom9.org/autogk.htm
Stand-alone DVD players with MP4 compatibility are just now becoming common so PC playback isn't the restriction it once was.