I Have a Question about Grand Theft Auto V

You actually forgot to ask the question.

Yes

Well, I don't live in USA, but where I am, your GTA V copy would be considered as an used game, not tradable with a new copy without pay a little bit for it, even on PC.

Depends on the store, but I really really doubt it, you would have a better chance getting it for Xbox One, also it is an upgraded form of GTA V with improved quality

It's already on PC, and I'm playing it :P here is proof, just kidding, and for the time you get a physical copy it will come with a code that activates on Steam.

I highly doubt you can get a 40-50 bucks game on pc for an used copy from 360. Best thing you can do is sell it in a gamestore or to someone in real life (personally, internet can easily turn into scams and you might get nothing in the end). Usually selling it to another person, might net you more cash than selling to a store, at least here it does. I paid 80 bucks for my 360 copy and preordered the pc version, if i sold my 360 copy, i would expect at least 35 bucks from an outsider deal.

you can trade it in but dunno how much you will get

Do you think selling a 10 year old Mercedes is enough to pay for a brand new 2014 Mercedes?

No. According to the CAG thread, the trade-in value for GTA V on 360 was $18 (6/30/14). Even if you managed to get a bonus 50%, you'd get at most $27. By the time the PC version comes out, I bet you'll get $10.