Christmas presente for an expert scubadiver

Hi guys, I'm asking for your help: Christmas is coming and I need to do a present to a person very close to me. He is 42 years old and has been doing scubadive for years. He is very passionate about it. I would like to give him a present about this topic but I really don't know what to do. The budget is around 50€ / 50$. I am not an expert in this field so I don't know what would be a nice choice.

Several years ago my gift was a subscription to a magazine about scubadiving and he really appreciated it.

At the moment, my idea is a Lego set about scubadiving but I'm not sure, since Lego sets have been a recurring gift in the family in the past years, so I would like to change.

Can you suggest me something?

Thanks in advance to whoever will answer.

EDIT: thank you all for your answers! They will certainly help me!