My almost 4yo understands perfectly well that things costs money, that some things are a lot of money, some not, and that the money comes from mummy working hard. And that it has to pay for essential things too.
I sometimes work from home, and at 3.5 she wanted a magazine and when I said it was too expensive, she asked if I could go home and do some work. Slave driver!
We've talked about not everyone being lucky enough to have a job that pays well, or a job at all.
We talk about that on daily purchases, but I'm leaving Santa for now. Although she knows that some things are expensive, she can't guess what. So she could get a £100 kitchen (she won't!) and a friend a big set of crayons from Poundland, and she wouldn't know which was more expensive. Bad example - she might choose bigger item! But you know what I mean.
Right now, what she REALLY wants is a sponge. A plain bathroom sponge. No consumerism here! (possibly helps that's she's never seen a TV add in her life)
Plus, I think she's too young to compare. So we're enjoying Santa. Whilst always making donations and explaining why she puts coins in the donation bucket, etc.
Yeah - she's a fortunate child, parents with some money AND lots of love. But I think it's OK to just enjoy that, and leave the injustices of the world for another year.
On a related note - when she had a tantrum over not getting her Xmas sparkly shoes to wear early, she was stopped dead in her tracks when I told her at 4, I had one pair of shoes, my brother's old ones.