what colour are they,if they are the usual off white they are almost uncleanable.if you do do them i would vacuum carefully with a brush attachment,mix up some pro chem fibre shampoo till suddy,use a clean tery towell or sponge, gently wipe acrooss the surface without over wetting. try one first see how it comes out,dont expect a great result.i have also done the same using dry cleaning solvent ,if you try dry clean method be careful of the backing of the blinds as they can come apart or bubble.
as far as price goes perhaps do on time basis,not gonna be a money spinner as the result is limited.
i used to have a dry cleaning bus and that was my method,hope it helps gary bristowclean
nb pro chems fabric restorer also good option but beware as it contains some solvent good luck !!!