You can spend a reasonable amount. Or you can spend a fuckton.
Have done both. I now do reasonable. By shopping mainly at Aldi. Which is half the price or more of M and S and just as nice, if not nicer.
Write a list. Plan your menu. Tick off as you buy stuff. Turkey crown and gammon go well together, look at the suggested serving size and don't go mad with sizes.
Veg, work out your portion sizes. Sprouts are cheap, as are carrots and parsnips from Aldi. Red cabbage is very easy to make fancy. I do mine in the slow cooker to save stove space.
Garlicky mushrooms, pate on toast, homemade soup or homemade prawn cocktail are all a fuckton cheaper than the fancy readymade starters and much nicer.
Buy normal desserts, and fancy them up with fancy plates or extra trimmings. But again Aldi has nice showstopper puds for half the price of m and s.
Ask guests to bring desserts and wine and any other booze.
I don't do Christmas day dinner for anyone other than us, but NYD I do a big, fuck off fancy dinner for 10 adults and 4 kids. Meat usually costs about £50, veg about £20, £20 on naice stuffing and piggys, £20 on 2 different starters and then £10 on pudding as guests all bring something. So £120 for 14, 3 courses. It's enough, and my guests all love my NYD dinner. It's grown over the years and I have a waiting list of people who would love an invite if any of our regulars drop out. We just can't fit any more in.