If you are wanting to buy your own drinks for the reception, some major savings can be made.
If you live within easy reach of the channel then the obvious choice is a trip to France. There are some very reasonable off peak ferry crossings and you can pick up some bargains. It is best to do your homework very thoroughly before you go. Check out www.tesco-france.com to see what they have available. Lots of the wines on sale are the same brands as in the uk so you can check prices. Check out www.ferrycrossings-uk.co.uk.
If however you feel that the cost of trip will out-weigh the savings, the best way to get bargains is to start looking early. Keep an eye on your local supermarket and buy when they have special promotions. January is a good time to stock up with champagne (though if you are on a budget, Cava is a better bet) and other sparkling wines.
If you are using a hotel or restaurant for the catering, do remember to check how much corkage they will charge if you want to bring in your own wine, it can be around £5.00 per bottle!