Steve,
While I agree that there are more "important" things than replacing curtains, I recently succumb to the urge to get rid of the 15 year-old rags that were partially covering the portlights on our E34. After much consideration, we opted for a really good looking Sunbrella materials (warm gold with a navy pin stripe) that complements the teak, the blue cushions and the cane trim. That said, we had the curtains made (original quote - $200; not that bad). With no alternative for hanging the curtains (I wish we had read Loren's post first), we stayed with the aluminum extrusions and had slides "hand-sewn" to the curtains (another $200). All said and done, we now have some beautiful curtains that fit, look great and -- since the materials is Subrella -- should last forever. Long story short, take a look at the available Sunbrella material and use Loren's method for attachment; should yield great results and relatively low cost!
Chris