The only time I ever paid, I think it was like £18 for a set menu (plus extra for drinks at the bar).
Honestly, I think if a company is having a Christmas party, it should be funded by the company, not by staff. Though I appreciate this doesn’t work for, say, the NHS, but I do think it’s appropriate for most organisations including third sector ones.
We have a party for our staff. We’re a small company. It’s a night away with an activity, dinner, drinks, taxis, hotel and breakfast the next morning fully paid for all employees. They also aren’t expected to work that day so get the day off work fully paid. Even if someone couldn’t come for whatever reason, they wouldn’t be expected to work that day.
If you want your people to feel appreciated, it’s not really an end of year treat if they have to pay for it themselves.
That said, if I really liked my co-workers, I’d probably pay for a meal and a drink, or I’d pay for a drink or two (I don’t drink alcohol anyway) and hang out. I probably wouldn’t pay more than that.