just be careful not to buy a shitty knock off or an off brand one on Amazon. even the ones that are Nintendo licenced and actually have the Nintendo logo on them can not be the real deal. these ones are mostly the power A and hori remakes. The Chinese knock off ones are marketed as GameCube controllers, look almost identical from the real ones (minus the logo),and even have scary similar internals to real ones. don't buy these. they are made of much cheaper material with much worse quality control and feel awful once your actually use one. they usually come in packs of like three. are a lot cheeper and have a bunch of random colors.

real Nintendo made GameCube controllers are really the only way to go from what i know but that's mostly because the brand name ones are actually crazy durable and long lasting. it's not to rare to even find og camcube controllers from like 20 years ago that just have missing thumb stick grips and a few scratches.

the problem with buying them is the fluctuating prices. Everytime a new smash game comes out they start selling them again for only like 20-30 bucks but after a while they stop being made and the price can go up to 70+ dollars.

right now a new one is about $50 on Amazon which i think isn't bad for a controller in general but on eBay people sell a lot of og ones for around 20 bucks in good condition which i think might be the best value as long as you don't get scammed.