For me, starting early is a mistake - I just go off the things that I have bought and end up buying twice or three times So these days I wait until November pay day.
I budget quite tightly. We told all our relatives some years ago that we would prefer not to exchange presents with adults any more. Most seemed relieved. Having said that, we do exchange presents with anyone we are spending Christmas Day with, and in many families that would be most adults anyway - in our case it's usually only 2.
DH and I spend £10 on each other, I spend up to £80 on one present for ds and another £30 on stocking presents for him - that's the one I find really hard to control, I loved my stocking as a child. I spend about £15 each on my four nieces and nephews, and £10 on my godchild. I have stopped joining in the Secret Santa at work. If we are seeing adults on Christmas Day I will spend about another £15 on each of them.
I spend about £30 on cards and the same on postage - I like cards and have quite a few overseas relatives, though fewer and fewer people are sending them.
I spend a total of £10 on wrapping paper, a pack of curling ribbon and sellotape (I think the really cheap stuff from the market is a false economy, but reuse wrap where I can, and always for the stocking presents).
I buy a tree for £20 - 30 and decorate the house with holly, ivy and the curling ribbon. Most years I buy a new bauble for £6 or so.
We have a food budget f £100 a week anyway - I try not to go too much over that, maybe another £40.
Last year we went to see a show in London and took nieces and nephews out - that all cost about £200 - can't afford it this year couldn't afford it last year either which I'm really sad about.
We do a Christmas charity donation of about £25.
Total £385. I'm leaving out cost of fuel though - usually travel to see at least one lot of relatives at Christmas - call that another £20.