Expanding the Atari 2600/7800/5200 interface

One concern I keep coming back to is cost vs. complexity.

This approach makes sense if you’re using multiple consoles, but for Atari-only setups the economics are less obvious — especially for people who prefer original hardware and controllers.

I’m curious whether anyone has explored lower-cost ways to expand the Atari 7800 controller interface without sacrificing compatibility or introducing latency. Most alternatives I’ve seen either add complexity or require significant compromises.

One option for a 5200 controller is the https://maker-matrix.com/ but like all good projects its dead. 

Question: Are there any simpler or cheaper interface expansions out there that actually hold up in practice, or does cost inevitably dictate what you get?