RE: Vorza or Nitro Buggy?
300-600 for just the buggy? If you have the budget build a kit. You can get a RC8B or a 8ight 2.0 for
under 500 add a N21Bf and a pipe for under 200 then a couple of decent servos for 160.
In the long run you will be much happier and spend less money than trying to upgrade a RTR
car.