Other than to say he won't need senior flex shafts, there is little to suggest. A full bag of new clubs is in the neighborhood of 2 G's. Depending on his experience and the competition for the golf team, you can get suggestions from the coach on who to work with locally to find something suitable to his level of skill. They can help you spend as much as you want for new clubs and offer suggestions for used clubs that will be appropriate to his game if he is not ready to dedicate as much or more time than to BB.

Just from Titleist alone, there are 8 different iron heads. To pick one for your son unseen is as reliable as buying a scratch card. A not-so-good idea is buying a set off the floor from someplace like Costco. They're for the average player and I've never met that person.

What does he want? Make sure he is part of the process - a person needs to feel confident when looking down.
Take him to a store and let him hit different models, get some data as to his results - get him educated. Not sure what you want to spend or how serious you kid is about the sport. Would suggest getting at least somewhat fitted either via a free demo day event or a $50-$100 local store fitting.