I thought about cleaning tack at our yard for some extra cash, but decided that it wouldn't be a good idea, because if I have a bad week with my joints, I won't be able to do any.
I was intending to charge depending on what people wanted cleaning, because some people have very simple bridles and others have all kinds of bits of leather hanging off - nosebands, martingales, etc. which take a bit longer. Probably about £3 for a bridle that was just the head piece, cheek pieces, bit and reins, and fifty pence per extra bit. For saddles, I planned to charge £3.50 for synthetic saddles and £5.00 for leather, as I find synthetic much easier to clean and most of it just needs a quick spray and a good brush down.