Need a couple hammers to start with too. A deadblow and a engineer's hammer. He'll need more later, but I would have trouble getting through a day without these.
I like the Nupla Powerdrive hammers. They're often rebranded for truck brands.
Lots of different engineer hammer options. I used an Estwing for a long time that I liked - and it was cheap. I lost it and replaced it with something different, Titan I think. I don't remember exactly because I hated it and bought a Stanley anti-vibe instead. The Stanley is even better, but is more expensive. Were I shopping right now I think I would choose the OSCA 3 or 4 lb. It's beautiful.
These might be a place to save the budget though - upgrade gifts for later dates perhaps. I remember the Titan I bought was like $11 for a two pack with a mini sledge. Super cheap. No reason your son couldn't get by with a cheap hammer to start.