on the other side, they have released games on PS360, it shouldn't be impossible. I think it would rather require to chop some features, e.g. how many cars you have in a race, maximum resolution, polygonal detail etc. Thus, most work would be content adjustment and a lot of QA work, +2 to 4 engineers, then maybe 6 months until it could go to some TRC check.
But to really evaluate this, you'd need to have a deeper look at the current state. Porting is mostly about solving problems, hence you first have to evaluate the possible issues and how long/costly possible solutions would be. e.g. if the UI is made resolution independent, you have no work, if the UI is made for 1080p+, you'd need to either find a technical solution to get it work, or some artist would need to redo it all and some QA would need to validate it (e.q. is all text readable).
There would be further maintenance cost e.g. multiplayer services, DLCs, etc.
edit: just happened to remember, there is a guy in another forum who offers porting services, ask him if you have a budget: Gamedev.net
if you are really serious, try to get in touch with some company that is specialized in porting games, e.g. Irongalaxystudios.com