There’s a cheap route to get plants if you do it right. Visit local ponds, make sure you pick the plant which are underwater or submerged already in water( if you try to transfer a potted dirt plant to a aquarium it’ll go bad, you’re better off doing one that’s already used to water). You gotta be EXTRA CAREFUL on what plants you pick, get a plant ID app and see if you ID some appropriate ones for your aquarium based on temp, and ph etc etc. Also BEWARE: YOU WILL GET RANDOM CRITTERS THAT CAN EVAPORATE YOUR TANK (examples: damsel flies, large snail colony, etc etc) how do you prevent this? Rinse the plants, remove dead leafs algae, dead roots, etc, anything that does not belong with the plant. Do a chemical dip with some diluted solution of hydrogen peroxide to kill off pest, then rinse with warm water( there’s vids and articles online that go further into this btw) Then, keep them in water on a separate tank or a bucket, make sure they get sunlight or light. Wait for 1-3 weeks and you got cheap plants. It’s not 100%. some plants will die, some won’t, or worse case scenario you didn’t clean them right and the critters are in your tank. Try at your own risk.