depends on where exactly the marriage took place - i.e. which parish and denomination.
Civil certs from the GRO are not online but Images of church marriage records for some areas are available (free) on the IrishGenealogy website - mainly RC and CofI. Church of Ireland marriage records for this timeframe show the same details as civil records.RC marriages show different details to civil records - again depends on which parish etc.
Transcripts (only - not images) of civil and church records for many counties are available for a fee on RootsIreland or other sites, but for about the same price you can order Research certs from the GRO, which are photocopies of the civil record in the register.
These cost €4 as long as you provide the full references from the BMD Index - i.e. name, year/quarter, registration district, volume number & page number.