One thing you should keep in mind here, something sort of counter-intuitive, is that narrow fonts aren't always/necessarily more economical (except for single lines). This is because wide fonts can be set at a smaller point size, maintaining apparent size (compared to a narrow font set larger), and saving space vertically. This is especially true if you have a lot of paragraph breaks (which eat up the potential savings of narrow fonts). Another thing is that serif fonts can actually be set tighter (I mean stem-to-stem, and wordspace) while maintaining readability (not to mention their inherent readability advantage).
Try Parable:
http://www.myfonts.com/fonts/fontfont/parable/
hhp