Personally, I would try to get a Commodore 64. A lot of them were produced, and while they cannot connect to all modern TVs, they do connect to pretty much any screen with RCA ports.

I also have a couple of non-answers for you that you and others may find useful while shopping for real hardware.

The most affordable way to code BASIC today is for free using X16 Commander Emulator or VICE. X16 has some nice quality of life features, but VICE runs pure Commodore BASIC.

For pure C64 Commodore BASIC, but with modern hardware, consider Bare Metal 64 on a Raspberry Pi.

And of course, for nostalgia consider TheC64.