Everyone should already know this, this is nothing new and there is no big secret to paying less for birth, marriage and death certificates, but I feel it cannot be said often enough. The cheapest and easiest place online to order copies of English and Welsh civil registration documents is the General Register Office website.
The Directgov website will give you all the details including cost, references needed, alternative methods of ordering and delivery times etc. on the Order birth, marriage or death certificates page.
Certificates can be supplied even if you don’t have the index reference (for a slightly higher price) but many of the indexes have already been transcribed on FreeBMD so it should be possible in many cases to find the reference yourself, free of charge also.
Birth, marriage and death certificates are one of the most important types of record for English and Welsh family history researchers, but please don’t spend a fortune on them, use the official website.