I hope not to step on anyone's toes, but I spent well over $1,000 to get dark ride images. Because it became an obsession, I analyzed all the options and here are my observations: The first requirement is a camera that is capable of usable high ISO (6400-12800). You may use less, but in some cases, this is what it will take. Second, you need a lens (on a crop sensor) in the range of 30-35 mm f1.8 or less. The current "gold" standard in this range is the Sigma 30mm f1.4. In the past year, Sigma has released a new model at an increased price, however if you can find the older model, I would jump on it in a heartbeat (I already own it). As far as the new Sigma 18-35 f1.8, this appears to be an answer to a prayer. This could be the ultimate dark ride lens. The announced price of $799 is way below the $1,000+ price that many thought it would be. I suspect that by the time your trip comes along, depending on demand, the price could drop as most do after a period of time. My opinion only, is that the eventual price will be in the $500-600 bracket. There has been some discussions about the lens weight. If you are intent on getting the best quality dark ride images, weight should be the last thing you consider. Better and faster glass weighs more, PERIOD. That comes with the territory. If your desire is to get better images than can be had from consumer (kit) lenses then weight doesn't matter, only the quality of the finished product.
Again, I don't wish to rain on anyone's parade, but better glass costs more and is heavier, Fact of life!