Aquarium keeping can be an expensive hobby, but you can build a great collection of plants for cheap by being a little patient. One example involves Java ferns, an easy to grow moderate-light plant that attaches to rocks and wood. The deadest, most decayed leaves will still sprout plantlets... given a little time you'll end up with a lush, fully plantscaped aquarium! Typically, I collect plantlets into a grow-out vase and leave them until they get a little bigger and can be used for 'scaping.
^^regular Java fern (Microsorum pteropus), plantlet sprouting from dead leaf.
^^just waiting to take over their corner of the world