Well there are many controller options: Wii Remote, Nunchuck, Wii U Pro Controller, GameCube Controller, Classic Controller, Classic Controller Plus, Nintendo 3DS. At least, those are what I can think of. If you want the GameCube controller, you'll have to buy an adapter for it, but they appear to be sold out in most places currently. A lot of people are gravitating toward the Wii U Pro Controller (doesn't require adapter), but that's $50 or so. Wii Remote should be the cheapest option though, unless you already have 3DS.
You also may want to purchase an amiibo of one of your mains, so you can train it and then it learns from you and counters your fighting style, but only get it if you don't mind losing. It also gains strength naturally leveling up even if no equipment is fed and the AI may not always make the smartest choices...
Edit: Oh, and welcome to Smashboards, hub for all us crazy Smash fans. Hope you enjoy your stay here.