Dry cleaners is a good option always did that myself and add a little 
on for myself..
Hi Clinton. Just back from a week in the Lake District so only just read your post.
This is something that has always interested me. In adding a little to the dry cleaner's bill, did it actually cover your costs of attending the property; driving to the dry cleaners; returning to the dry cleaners to pick curtains up; return to custy's to re-hang curtains? Or was there another way of considering the deal?
To my simple way of thinking all your work could easily take at least an hour. So going by the rule of thumb we see on the forum you should be charging at least £50 and then perhaps upto somewhere nearer £100 on top of the dry cleaner's bill?
Of course if there is no other work around then "a bird in the hand is better than 2 in the bush" and so any profit margin is I am sure acceptable if it covers your fixed costs but if you find you are creating extra work which involves working harder/later than you would wish, is your strategy a good one?
I ask not because I am trying to be clever but simply because I could never make my mind up about it and in the end just decided I had enough work with carpets and upholstery to not worry about the hassle of it. If somebody was insistent about getting curtains cleaned I did then refer them to a dry cleaner who would collect them etc and in return they recommended work to me.
I look forward to your thoughts.
Roger