Yeah, he's probably down to his last couple of copies of Sapphire.
$150 is a horrible price. I'm not sure I remember anyone paying that much for the boot unless they thought it was real. Hold out for $60, although that seems kind of crazy IMO as well. I payed something like $40, I think.
As for what your first Arcade Card game should be...its tough if you don't like Geo games since those are its strong point. At least get Fatal Fury Special since its cheap as hell and one of the best.
Strider will not blow your mind. I'm not a big Strider fanboy, so I haven't compared all the versions, but you might as well have the Megadrive version from what I've seen.
Sapphire is the best overall game for the AC.
Popful Mail underwent a massive transformation for the MegaCD. The PCE version is a lot like an old computer game. The characters are square and the screen is cropped and all that. I'm not saying to not buy it, I'm just letting you know.
3x3 Eyes has the most impressive 16-bit cinemas (the opening at least) I've ever seen. If you can get it for $10 or whatever, do it, just for that. Its a digital comic though, so don't expect to have much fun with it, regardless of what languages you speak.
Honestly the Arcade Card is kind of like a less sucky version of the SuperGrafx. They both do some impressive stuff, but the best PC Engine games are Super CDs.