PCE EverDrive shouldn't cost near ED64 as Krikzz said and because the hardware involved is more like the EverDrive MD, perhaps even less. Krikzz said before it would probably cost similar to the EverDrive MD and I believe him.
Now if you wanted to add features like Arcade Card support then it would cost a whole lot more. But it should be kept simple (and cheaper) and focus on just running HuCard games. As I said before the only benefit to Arcade Card support is for American Turbo DUO/TurboGrafx CD owners who would need an adapter to use the real Arcade Card, but would not need one for PCE ED.