A useful site Charon, especially for someone who may be just starting out.
Something I read on another forum that is along similar lines to this - there are sites out there that will charge you the earth to get a certificate for you. There is no need to use such sites even if you are overseas. As long as you have the relevant informatiom (index references preferred) you can buy direct from the GRO via their own site
http://www.gro.gov.uk/gro/content/ at a cost of £7 per certificate (the price quoted is as published on the GRO website today). There may be an additional cost such as postage if you are buying from overseas.
They also have the option to phone or write to place an order.