Just FYI, lathering isn't necessarily a good thing. They add chemicals (SLS) to shampoo that do nothing beneficial, they just make it lather.
Shampoo is designed to strip oil more effectively than body wash, so it's not great for your skin, but if it doesn't bother you, then who cares. My skin would literally start peeling if I did this.
If the bar soap is overall cheaper, I would stick with that for your body. Shampoo is mostly water, so I can't imagine it's less expensive in the end.
Your soap will last a lot longer if you don't bother trying to lather it. Just swipe it over the area you want to clean, rub, and you're good. Trying to lather soap is a waste of soap.
If you really want to cut down on products, try washing your hair with just water. There's absolutely no need for most people to use any kind of harsh detergent on their hair.
Just bar soap for your body and water for your hair would be much better for all of your tissues overall rather than using a cheap, SLS filled shampoo that isn't good for hair, scalp, or body skin.