My boys got the Mario K'nex set for Christmas. At first they got a bundle from Target until we realized it was just a piece or section and not a full track, plus it had 2 pull back cars and 2 motorcycles (which we already had) and then an expansion pack for around $100. So we went to Toys R Us and found this one for $99.99 but it is a full and complete track. It came with two battery powered cars. If you buy the cars individually they are just pull back and release. The cars that come with the track are battery powered and go around and around the track. This track offers multiple obstacles like the fireballs. It is a HUGE set. It takes up a lot of space-luckily we have a basement so we can keep it together because it also takes a LOT of time and patience to put together. The kids love it. I would recommend rechargeable batteries because they go through batteries really fast. You don't really need the extra track pack or any other add-ons if you get the big track. By the time you buy an expansion track pack and a few of the obstacle tracks it just makes sense (for the price) to buy a set.
This one is only $59.99 at Toys R Us. It is smaller, takes less time to put together but still comes with 2 battery powered cars. It is Mario and Yoshi at the Finish Line