I don't agree that the GameCube's graphical prowess was its biggest selling point. Competing on tech has never been Nintendo's thing, if we saw them attempt such a strategy today, you might as well start nailing down the lid of their coffin.
That said, I do agree that the GameCube is great, and totally worth playing. For those looking for an innexpensive GameCube solution, your best bet is to acquire an earlier-model Wii. The component video support for the GameCube was decent, but required a proprietary cable that is extremely rare and expensive. The backwards-compatible model Wiis are comparably quite common, and acqiring a Wii component cable is cheap and easy. (or just getting an HDMI dongle) So getting nice, crisp progressive-scan GameCube support is much easier by getting a backwards-compatible Wii. At this point the Wii is also not very expensive on the second-hand market.
I also agree that the GameCube had a surprisingly comfortable controller. It was a bit atypical, but the design was actually quite forward-thinking, with memorization and usability at the forefront.