Personally I would sell the 240sx, depending on how the car is and drives good you can maybe get $2000-$2500. That leaves you with 12,000-12,500.
Now you can either get a really nice Kouki or just buy a R31. If you can find a R32 for that price psh go for it, but then again you would have to wait till the summer of 2014 to drive it legally.
Good luck.
