DDPDOJ goes for $350~$400, if I'm not mistaken.
Yes, there is a possibility that Futari may get ported to the 360. But if it does get ported it won't happen for at least 1 year, and quite possibly 2 years or more from now. So you have to ask yourself if you want to wait that long (and again, it may never get ported at all, just like many older CAVE games).