As far as I know, you have a year to import the vehicle. I may be wrong tho.
You'd have to check with the company who provided you the loan for your car to see if they accept you use the car in the US for an extended time. I know when I had a leased car, there was a specification in my lease saying that I was not allowed to use it outside Quebec for more than 30 consecutive days. If I was to, I needed a letter showing that my leaser approved my trip. (Kinda wild but I understand why they need to do that).
I do not know the cost of importing your car. (I know I can't import mine so I'm just going to sell it)