If you are travelling from the UK there are flights throughout the day from both Bristol and Birmingham to either Knock or Dublin Airport. Just be aware that Ryanair only release flights for the following 6 months so they may not be available until the New year.
There are regular bus services from both airports to Galway, with Knock to Galway taking approx 1hr40 and Dublin to Galway approx 3hr. Each coach service will take you to Galway Coach station, a five minute walk from the Wedding Venue. Tickets are easily available via www.busbud.com.
If you are looking to hire a car you can get comparison quotes from a number of sites via a google search however www.Kayak.com have consistently been the best value from our experience. It usually pays to book a few months in advance to get the best rate possible.
Accomodation
Galway has plenty of Hotels and B&B's to choose from. If there is a larger group of you travelling together it may be worth looking at Air B&B for an apartment / house to share during your stay. Just ensure you check the distance and travelling times to the venue to ensure you don't get caught out. www.Trivago.com and www.Booking.com will show all available accommodation.