There was 32. (Including bride and groom) at our wedding 10 years ago. Civil wedding at a country hotel and golf club.
I know my flowers were £400, dress was £400, civil wedding etc was about £200 (this may be excessive as I could be wrong!), £500 for photographer (got disc too) and I think it was £52 a head for the wedding breakfast and £70 for room hire and then £150 for evening buffet (no evening do except a roommate hire).
My parents paid for some of it so I think with everything in including some overnight stays for some people it was about £10,000.
Lots of people book 2+ years in advance so they can spread the cost (pay for stuff early or pay monthly)
TBH I believe most people take out loans and/or ask bank of mum and dad! We were able to pay for our own wedding but my parents insisted on helping financially.
When we were making the finalisations to our wedding there was a wedding on that had 150 day guests and 300 evening guests.
I figured alone it was about £8,250 at least for the day ceremony etc not including the evening room hire (£300 I think for the largest which they would need plus DJ hire at least and buffet would set them back a few grand), wedding attire, rooms, flowers, photographer (they had a videographer too) and they invited their cousins and their parents neighbours!!!
I suppose if you want a big wedding and have the means to pay for it, go for it, but if not then plan according to your budget.
At the end of the day, you have a marriage and you make it what you want it to be!