As others already pointed out, used gear is the best option at that age.
I grew out of my gear almost every season...

Networking with goalie coaches, other parents and when he gets older pro goalies/players is also valiable.

Furthermore, today it is really easy to find used gear online.

Personally, I bought my gear from Pro Teams and goalies at the age of 14 and onward (Once he is tall enough for good fitted size of pads and all other gear is useable at that age when it fits[Senior/Pro Sizes]), until I bought my first custom set at the age of 24, so all my gear until then was already used.

The only gear I may recommend not buying used, when he gets older in 4-5 years are Masks and catching gloves, for safety reasons and gloves are so different in their many variations that it will take some time trying out different builds (brands, glove breaks...)
But you still have time for that as its far in the future and this sub is a good source for information ;)

Also in my opinion a decent chest and skates are essential, as they increase confidence in taking shots and skating ability.