I'm going to one tomorrow actually!
I've looked up the place where it is on t'internet. For the particular venue they've chosen it's £209 per guest, provided there are over 120 of them. So, that's £25k straight away, assuming there are 120 of us there. The venue can take up to 290 so you might be doubling that! That's before wedding dress, usher's outfits, hired entertainment, cake and various other extras.
On top of that, we've all been offered a room at the hotel paid for. Their cheapest standard tarif is something like £230 so you can probably add on anything between another £20k - £50k.
Basically the whole thing's going to cost an utter **** load. Mental really but I intend to enjoy myself!