We're in the process of organising the IL's 45th wedding anniversary, and we were originally going to pay for it all ourselves. But since our circumstances have changed, IL's suggested we ask people to pay for their own meal in lieu of bringing gifts. We're putting it on the invites, so people can decide for themselves whether they want to come or not - this is what we've put:

'After 45 years of marriage, - and - would appreciate that each person pay for their own meal and drinks, in lieu of gifts'

I've got this on a separate card to the invitation, being sent out at the same time. Then I've mentioned the cost per adult, with the entree and choices for mains. If I get a job soon we'll be able to set up a drinks tab, which will be announced on the night, but if not, at least people are prepared, KWIM?

If you mention it on the invites, then people won't have to assume. At the end of the day, whether they come or not is up to them