Here's another simple, rather obvious tip for your budget: Bar soap costs less than liquid soap. It also lasts longer and its packaging produces less waste. To help your bar soap stretch even farther, remove the package and before use let it dry out for at least a few days. (Each time we start using a new bar, we remove the packaging of the next one, so it has several weeks to harden). This makes it even more longer-lasting and creates less soap scum in your soap dish. And speaking of soap dishes, my favorite is one with slits in it that allows for drainage into a lower dish, so the soap itself never sits in water to become soft and gross.
But what about the "ick factor" and potential skin-drying of bar soaps? Or the superior convenience of liquid soaps? In addition to the above-linked article (which is excellent and succinct), check out this one for answers to these questions and more.