Weddings cost what you are willing to pay! Abroad is only cheaper because there's fewer guests and less fancy than most U.K. weddings.
Mine is coming in at £4,500 all in - church, dresses, cake, car, photos, exclusive hire of the top floor of local gastro pub, musicians, food and drink. 50 guests. To get it for this price we are using local businesses we know, walking distance from home for reception, negotiating hard, student for photography, local baker etc. oh and he's wearing his own suit, as is best man (buying them matching ties and hankies though that match bridesmaids, all bought online). We could have saved a further £1500 by just having a meal at a local restaurant, no evening reception, but we know the musicians well and wanted them specifically.
Honestly abroad like for like isn't really cheaper as there's hidden costs like your apostille certificate (yes had to look this up for a family member) extra luggage etc. Santorini isn't cheap either.
Have the wedding you can afford, obviously but I can't imagine this coming in cheaper. The cheapest option I found was church (or registry office) followed by back room of local club (once conservative club I believe) who quoted £100 to rent the room for the day as long as we didn't bring our own drink in! Local catering firm quoted £20 per head for a hot and cold 3 course buffet, plus cheese board and charcuterie for evening snacks.