The Gemara says that one should only eat meat once a week, on Shabbos night. (Chulin 84a). Given the story in the Gemara about the son who told his mother his father wanted peas when he really wanted lentils and vice versa in order to preserve shalom bayis (Yevamos 63a), it seems that people then got most of their protein through legumes. If people did that today they would save a lot of money, and enjoy better health to boot.
Regarding jewishfeminist’s comment about having kids and the parnassah following, many people believe very strongly in that teaching. The idea is that each child has a source of parnassah that actually comes with it into the world. I don’t know the source, but I’ve read things by rabbis who discuss and endorse it (such as Rav Shalom Arush). In my own family we did not wait until we had a good income before we had children.
It’s true that being Orthodox is expensive, at least in the US. I don’t know how people with average incomes manage to get by AND consistently save money for retirement. But with G-d’s help and good planning, I’m sure it can be done.