We have straps from £5.95, bracelets and expanders from £9.95 and we have never charged for fitting. What a cheek that would be.
Neither do we charge for taking links out of a bracelet or expander that we have sold. That said, we do add a bit to the retail price of the expanders, because they are a bit of a pain to adjust and you can pretty much guarantee that you'll have to do it. We wouldn't charge for adjusting a bracelet on a watch we've sold either.
On a customer's watch:- a single bracelet link removed costs £3.95, two or more £5.95, as there's no more work involved in removing 4 links than 2. Expanders are £6.50 no matter how many links we take out. We don't charge again if it needs readjusting, because sometimes the customer needs to live with it for a day or two while they decide if it's still too loose.
For batteries we charge £6.40 for a 1.5v battery in anything with a 'pop off ' back regardless of watch quality, £7.50 for anything with a 3v battery or with a threaded or screwed down back. If the existing battery is still full voltage, we don't replace it and do not charge.
Customer relations is all in this day and age. Treat them right and they'll keep coming back and will recommend you to their friends, which is worth far more than charging a few extra quid for fitting a strap you've sold them in the first place.