I have a Commodore 64 that I acquired from a junk shop for $5. The C64 does not have any kind of RGB video output, and I don't have a suitable monitor or TV set with a composite video input. However, I had some parts salvaged from the colour circuitry of an old TV set, so I decided to try building a PAL to RGB decoder. I was mostly successful.
I have put a full schematic and a discussion of how it works and what I learned during development on my web page, see the Project Writeup link above.