Quality over quantity. Definitely. I love the part about your makeup. Mine lasts forever, too, since I only put on a little bit if I'm going somewhere where I might be seen by someone I know, and I only do the whole shebang if I'm going to something really fancy.
I spend the most on concealer. I get this really high quality, all natural concealer that is like freaking magic. It costs $25, but it lasts ages.
Splurge and treat yourself, or you might lose motivation (I know I would), but definitely invest in yourself. It's excellent advice. Not just in your business, but in your health and emotional well-being, too. They are all among your most important assets.