When I was in STL I ended up workcamping, the owner had a side business doing Ultra Sonic Blind Cleaning. Mostly did miniblinds, but, the process worked really well on Day Night shades, vertical blinds, and also the front curtains, as he let me use the machine to do all of mine.
Most major cities have some sort of Blind Cleaning business that uses this technique, and he was cheap at about $10.00 a blind if you removed them. The ultra sonic process uses Piezo electrics that "Blast" off the dirt while the blind is submerged in a solution of mild detergent and water. It is truely amazing how much dirt comes off them.
A common trade name used is "Shine a Blind" which is the MFG of the machine. If you get through Saint Louis, I can hook you up with George, but I do know many other cities have similar businesses. We will do that again when we need to clean ours, as it works very well and doesn't destroy the fabric.
John