A few notes, both for yourself and anyone that comes across this in the future:
There are multiple versions of the PC Engine, both under that name as well as other names (Core Grafx, Core Grafx II, PC Engine Shuttle, etc)
The TG16 CD modules are breaking down at this point... there's a problem with the laser and alignment (an easy, if time-consuming and tedious fix), and also with some plastic gears that are breaking. Someone on pcenginefx was working on replacements, but I'm unaware if anyone ever got that far.
Pretty much the entire Turbo Duo line, both the US and Japanese variants, suffer from bad caps. If you get one of those (and it'll cost you an arm and a leg), do be prepared to recap the motherboard (it's all SMT aluminum cans). Ditto on the Turbo Express/GT handheld systems. If you don't recap the board, you can/will have problems with both audio and video, and of course, the electrolytic will eventually damage your motherboard. So far as I know, the Turbo Grafx 16 and PCEngine systems don't suffer from this.
The new PAL Turbografx units you see on eBay are pretty and they play NTSC games natively (i.e. you need to region mod it to play Japanese hucards). But they will not play NTSC games at full speed due to the 50hz PAL standard (NTSC is 60hz). While a look at the motherboard indicates that these are simply modified NTSC boards, no one has yet been able to reverse the 50hz modification to set the board back at 60hz operation. In addition, RGB/S-Video mods for this system differ significantly from all other mods. All this in mind, I'm still quite tempted to pick one up
The cheapest entry into this arena is typically a TurboGrafx16 system with gamepad and PS (figure $60 USD range). TG-CD will usually tag on another $100 USD. Then game prices vary. Mods are out there for tapping RGB and S-Video, though the RGB will require an amplifier circuit (these aren't difficult on the NTSC TG16 systems, though it gets slightly more hairy on the Japanese counterparts). Region-switch and switchless mods exist for playing both NTSC and Japanese hucards on the NTSC systems - these mods are slightly more hairy (lot of solder points).
PCEngine systems purchased from within the US typically pull a premium. In many cases, it's almost cheaper to just order one from a Japanese seller and just pay the shipping.
There are flash cards available for these systems as well that support patching games via software to work in either region system (in some cases, this is a small switch on the flash card itself)
