Food: so eat less meat, it’s healthier that way — kosher vegetarians don’t have a significant economic penalty
Clothes: probably costs less to be well dressed – no need for $1000 suits except maybe on Shabbos – fashions change very slowly – if you were respectable in Boro Park 30 years ago, you can still go out in public in the same clothes
Communal fees: they are all need adjusted — most shuls don’t charge unless you want to reserve a specific seat for three days a year, and the fees are tiny compared to Reform and Conservative
THE BIG COST: is the “opportunity costs” of spending time learning instead of making money, and being limited to Shabbos-friendly job, of inability to take advantage of most non-need based scholarships (which it turns out are tied to athletics or military service), having to live in a city with at least basic Jewish services (kosher food, mikva, shul)
The also the expense of having children — Secular Jews have few if any. We spend most of our discretionary income on the kids. They have poodles, we have kinderloch. Fair choice. And I’ve yet to hear about a poodle taking care of you in old age.