The acceptability does not relate to the value, so the issue is the same whether it's worth $100 or $500: Can it be seen as having been given to influence you unduly?
The value is a factor, of course, because a reasonable person might think that a gift worth $500 is more likely to sway you than a gift worth $100 or $50, and it's only declared when it's valued at $200 or more. Members do not usually come to tell us about a gift that's valued at less than $200. They don't. Sometimes they do; sometimes they don't. Invitations are the classic case—to an event, to a show, or to a banquet.