The Duo-R and -RX are more reliable than the black Duo consoles... but as has been said you can't play US Turbochip games without a mod... so here are two recommendations:
For pure cost-effectiveness: a Duo-R for Japanese HuCard games and CD ROM games, and a US TurboGrafx-16 for US Turbochip games. Should be able to get both for a total of 150-200 A big drawback to this setup is that TurboGrafx controllers and Duo controllers are not interchangeable.
For the whole library: a US Duo for US Turbochip games and CD-ROM games, a SuperGrafx for Japanese SuperGrafx games and Japanese HuCards, and a Super CD-ROM2 add-on for a backup to your Duo for CD-ROM games. You should be able to get a US Duo and SuperGrafx for a total of 250-350, and a Super CD-ROM might add another $100.