You should be able to get a free trial membership from
http://www.ancestry.co.uk .
All you will be able to access, however, are indexes of marriages and certain other records. A marriage index is arranged by chronological quarter and so will tell you only which approximate month of the year a wedding took place, which registration district it took place in, the surnames of the couple and a reference number, which will guide you to the location of the marriage record in the actual registers. To get a copy of the marriage record (a marriage certificate) then you will need to apply to the appropriate register office with the appropriate fee. This is a national thing - you will not get one for free.
Ancestry.co.uk will, I think, allow you to search records such as parish records if you're a full member, and I think you can pay on piece-by-piece basis.