Math, just because the curriculum that I like is so expensive. If the curriculum that I really liked for reading, spelling, grammar, etc was as expensive as math I would buy it. To me it's not a matter of cost, unless I can't afford it ;), but a matter of is it going to work for me and my family. Sometimes the cheapest curriculum is what works out best in the end. It doesn't mean that because it has a cheap price tag that it's inferior to the million dollor ;) curriculums out there.