If you buy a UK birth, marriage or death certificate directly from the government the current cost is £9.25 and this can be done online. However there are many genealogy and other sites which will place your order for you in return for a high premium! Such sites are often quite secretive about how much they charge until you have typed in your order - although I must praise official-certificates,co.uk as it is easy to find out that they charge £16.95. (The basic rule is that if the URL does not end in .gov.uk you are almost certainly being charged well over the basic price for a certificate.)
But £9.25 is still very high and the reason is that the government will only provide certified copies - which are official legal copies of the type you need if, for example, you are applying for a passport, or if you are trying to prove that you are the heir to an unclaimed estate. The fact that your great great great grandfather is not eligible (for reason of death) to be able to apply for a passport makes no difference - the govermnet will not supply a simple photocopy of the original register entry - it has to be certified ...
At the moment there are two e-petitions asking for the law to be changed so that genealogists can get simple copies at a lower price, rather than certified copies. If either of these petitions gets 100,000 signatures the government has to take notice - which unfortunately doesn't mean they have to change the law.
If you would like certificates to become cheaper sign both the following petitions: