You have quite a few
types of coins to select from. One consideration is how much you want to spend.
Extremely relevant coins could run anywhere from less than $50 for a nice early copper
prutah or lepton, up to thousands for a silver
zuz (~
denarius) or
shekel from the
Bar Kokhba rebelion period, or any
price point in between.
In my opinion, one coin that might be a
good idea would be a half
shekel or
shekel minted in Tyre. These coins are generally agreed to be the only coin accepted by the Temple in Jerusalem for payment of the annual tax by every
Jewish male. Each male
had to pay one half
shekel, annually. Such a coin might give him a sense of connection to the Temple. They can be a
bit pricey (often more so than the
shekel denomination is), so again it depends on how much you wish to spend on the gift.
Browse through some of the posts in the
Biblical & Judaean Coins topic. You may get other ideas from there.
Craig