We have a Secret Santa in my immediate family (6). We agree on an amount that nobody is allowed to go over. And we use an online program to select who buys for whom. You punch in the names and hit enter and it selects a recipient for each person.

Simple. You only buy one gift. Job done. My wife insists on a small stocking for each child (3 of whom are in their 20s), which has a few small items like chocolate, a gag joke of sorts - usually played on Christmas Day, etc. She collects the items over the year as they mention something.