There are tricks.
Gravel and sand come from pool stores.
Rocks come from wherever clean rocks are lying around.
I choose plants that thrive without expensive ferts or CO2.
Driftwood comes from dead hardwood, soaked for a few months.
I don't ever touch salt tanks.
Tanks are often sold second hand.
Fish cost what fish cost, and there, I have generally managed to break even with aquarium related work. That is always a problem.