For what it's worth, the In-Time desk on the first floor of Debenhams in Oxford changed the battery and seals in my Aerospace a few weeks ago for £93. The chap there seems to be very knowledgeable and even gives you a voucher for a free coffee upstairs while he does the work, which is guaranteed for 18 months.
Breitling charged me £282 a few years ago for essentially the same thing and took six weeks to do it.