What do I have to look out for when buying a Gamecube?

I'm considering buying a Nintendo Gamecube. But I have a lot of questions.

1. Is the Gamecube still worth it? I have a Wii, Switch, DS and a 3DS.

2. How much does a Gamecube, games and controller cost?

3. Which games are good for playing with friends?

Why do you want a GC if you have a Wii that can play GC games?

No. The thing is ancient for playing it is not worth it but for collecting yes.
30-40 euro
Tony Hawk, Mario, Sonic, etc.

If it is not one of the last then there are two types of Wii and one of them can't play GC games, no mean not the Wii mini

If you want to play games that are only available on GameCube, then around 50 euro for a console with controller and cables, games range from 1 euro to 300 and above