I think the most fun, and cheapest way, to add plants is to get some Bulbs. They are like 3-4 bux for nearly 20 bulbs some times. All you do is shuv them in your gravel and wait! Once they sprout they will sky rocket! Yes it take time, and you must be patient. I think its well worth it though. Some plants could be 10 bux + and if they die... your out 10 bux! Coulda bought a new betta with a vase! haha. Also most bulb companies give a 30 day garentee, if they don't sprout send them back and they will give you new ones! Once i planted one tank, i dont think ill ever go back and buy another stupid fake one again! What a waste of money....
Good luck!