It varies from district to district. Charges are generally shown on the registry office's website. They usually ask for an SAE and a cheque for payment. It's always cheaper than going through GRO, though. (I think some registry offices in London don't offer this service at all, in which case you've no option than to use GRO.)
Well I rang my local register office and was gobsmacked by the answer I was given...............if I turn up and want a copy whilst I wait - £18, if I turn up and give them the details they can post it out the next day - £15, and if I ring up, pay over the phone, and can wait up to 10 days for posting - £9.
craft, your folks must come from somewhere dead posh then as that is pricey ;-)
Although GRO now charge £9.25 for their basic service - it went up last year, I think