you could say( and if i get this wrong someone please correct me, my spanish is not what it shoud be, you would think with 2 semesters and an "a" and "b" in the class i could speak better spanish...) cuanto es el banano?(how much is the banana plant) and if you want to buy banana fruit you could say: cuantas es las bananas? there are accents over a few letters but i dont have my keyboard set up for it.

( im getting the rosettastone for my spanish, i might actually learn something usefull)