Lol, I see I replied back in 2008 about the Polaris we bought for my son, and I have to say he is STILL riding it to this day, so I guess it was money well spent. I know you would save quite a bit buying a knockoff, but I know lots of people who bought them and they didn't last even a full year, plus they couldn't find people to service them.
If I were you I would look for a name brand used one. You may can find one from someone whose child has outgrown theirs and are looking to sell. Good luck!